October 2020 update: Democratic control of the Senate looks increasingly likely

Democrats are poised to do extremely well when voting concludes on November 3, 2020—just 16 days from now; as I write this, more than 26.5 million votes have already been cast, which is 19% of the total 2016 turnout. They are a near-lock to continue to have a majority of members of the United States House of Representatives (“House”), and their presidential nominee, former Vice President Joseph R. Biden, Jr., is the clear favorite to win.

And then there is the United States Senate (“Senate”). Currently, there are 53 Republicans, 45 Democrats and 2 Independents who caucus with Democrats in the Senate. To regain control, Democrats must either win a net total of four Senate seats OR a net total of three Senate seats while winning back the presidency; as president of the Senate, Vice President Kamala Harris would break the 50-50 tie.

As of now, Democrats are favored to regain control of the Senate. This conclusion is based upon a political climate strongly favoring Democrats—they lead by 7.2 percentage points on the generic ballot[1]—and all publicly-available polls conducted since January 1, 2020.

Before continuing, here is the October 2020 lighthouse photograph in my Down East 2020 Maine Lighthouses wall calendar.


In a previous post, I detail how I calculate and combine…

  1. “Expected Vote” (how a generic Democrat would fare against a generic Republican given state partisan lean, incumbency and partisan climate) and
  2. My weighted-adjusted polling averages (“WAPA”), which average two versions of WAPA: one treating all polls from the same pollster as statistically independent and one calculating a time-weighted average for each pollster

…into a single projected Democratic-minus-Republican margin and the probability the Democrat wins. As of now, the latter accounts for at least 89% of the projected margin in the Senate races assessed with a publicly-available poll at least once in 2020; in the six states with no polling,[2] the Expected Value is the projected margin.

Table 1 reports two projected Democratic-minus-Republican margins and Democratic win percentages for this year’s 35 Senate elections: one using all polls conducted since January 1, 2020, and one using only polls conducted since the two national party conventions. I now weight all polls conducted after August 28 (the day the conventions ended) and before September 29 (the day of the first presidential debate) 1.5 times higher than previous polls, and I weight all polls conducted entirely after September 29 3.0 times higher. The table is sorted by likelihood the Democrat (or Independent Al Gross in Alaska) wins the election, based upon all 2020 polls.

Table 1: Projected 2020 Democratic minus Republican margins and likelihood of Democrat winning calculated two ways

StateCurrent PartyMargin since 1/1/2020Dem win%Margin since 8/29/2020Dem win %
Rhode IslandDEM29.4100.0%29.4100.0%
New JerseyDEM23.9100.0%24.3100.0%
New MexicoDEM10.799.8%9.999.7%
New HampshireDEM14.499.8%14.199.8%
North CarolinaGOP5.094.1%4.893.5%
South CarolinaGOP-3.116.9%-2.324.4%
South DakotaGOP-21.20.1%-21.20.1%
West VirginiaGOP-20.60.0%-20.60.0%

Georgia Republican Senator Kelly Loeffler, appointed by Governor Brian Kemp in December 2019 after Senator Johnny Isakson retired, is running for reelection in a “jungle” primary in which every candidate, regardless of party affiliation, appears on the November 3 ballot. If no candidate tops 50%, a runoff election between the top two vote-getters will take place on January 5, 2021. Republican House Member Doug Collins of Georgia is also running, as are Democrats Raphael Warnock, senior pastor of Ebenezer Baptist Church in Atlanta, Matt Lieberman, son of 2000 Democratic vice-presidential nominee Joe Lieberman, and former United States Attorney Ed Tarver. I calculate WAPA both for the all-candidate election on November 3—polls of which strongly imply either a Warnock-Loeffler or Warnock-Collins runoff—and hypothetical head-to-head matchups between the top two Republicans and the top three Democrats, combining them into a single “Democrat vs Republican” average as follows:

  1. Calculate averages, weighted by number of publicly-available 2020 polls, of the Democratic margins over Loeffler and Collins. Based on 11 total polls, Loeffler is about 3.6 points behind the top three Democrats, while Collins is behind 1.5 points based on nine total polls.
  2. Take the unweighted average of the Loeffler and Collins averages
  3. Calculate a final average “Democratic vs. Republican” margin, giving the head-to-head matchups twice the weight of the “all candidates” WAPA


Let us examine these 35 elections in groups.

Safe Democratic (10). Senators Edward Markey of Massachusetts, Jack Reed of Rhode Island, Richard Durbin of Illinois, Cory Booker of New Jersey, Chris Coons of Delaware, Jeff Merkley of Oregon, Mark Warner of Virginia and Jeanne Shaheen of New Hampshire should easily win reelection by double-digit margins, while in New Mexico’s open seat House Member Ben Ray Lujan is expected to beat meteorologist Mark Ronchetti by around 11 points. First-term Senator Tina Smith of Minnesota is now a clear favorite as well, with a final margin around nine points.

Likely Democratic (1). First-term Senators Gary Peters of Michigan is considered vulnerable because he represents the closest state in the 2016 presidential election. And when examining only the “polls are statistically independent” WAPA, Peters’ margin has dropped sharply from 9.6 points through the end of the conventions to 5.5 points since then. Nonetheless, I expect him to prevail over businessman John James by low-to-mid-single-digits.

Likely Democratic flips (4). Four incumbent Republican Senators—Cory Gardner of Colorado, Martha McSally of Arizona, Susan Collins of Maine and Thom Tillis of North Carolina—appear headed for defeat by single-digit margins; these margins changed little pre- and post-conventions, with McSally gaining 0.9 points and Collins losing 1.6 points. McSally and Gardner are the most likely to lose—by high single digits—to, respectively, former Governor John Hickenlooper and former astronaut Mark Kelly, husband of former Arizona House Member Gabrielle Giffords, who was shot and severely wounded in January 2011. Collins and Tillis, meanwhile, trail Maine Speaker of the House Sara Gideon and former North Carolina State Senator Cal Cunningham, respectively, by around five points.

Lean Democratic flip (1). Based solely on expectations—incumbent Republican in a lean-Republican state running for reelection in a strong Democratic year—Senator Joni Ernst of Iowa entered this election season no better than even money to win reelection. And now she trails businesswoman Theresa Greenfield by just under three points, with Greenfield’s margin increasing by 1.6 points after the conventions. This is enough to make Ernst a modest underdog—and this debate flub is likely to hurt Ernst even more.

Toss up (1). The Georgia special election is extremely difficult to assess, as I wrote earlier. Depending on which set of polls (all, or only post-conventions) we examine, the Democrat is either a one-point underdog or a three-point favorite—and that assumes a Democrat, as now seems very likely, makes the January run-off election. Given the extreme uncertainty surrounding this election, I consider it a toss-up.

Likely Republican flip (1). While Alabama Senator Doug Jones is outpacing his fundamentals—running as a Democratic incumbent after only three years in a very Republican state—by 9.6 points, he will almost certainly lose to former college football head coach Tommy Tuberville. In fact, losing “only” by mid-single-digits would be a moral victory for Jones.

Lean/likely Republican (4). There are four Republican-held Senate seats—in states averaging 16.8 points more Republican than the nation as a whole—which Democrats have between a 17% and 28% chance of winning, using all polls conducted since January 1, 2020; Democrats trail in these elections by an average 2.5 points. The outlook improves slightly when only post-convention polls are examined, with the average deficit dropping to 2.2 points.

Going from least to most likely to flip:

–In South Carolina, former state Democratic Party Chair Jaime Harrison has closed the gap with Senator Lindsey Graham from 4.0 points pre-conventions to 2.0 post-conventions, but still has only about a one-in-four chance of winning. Notably, a Harrison victory would give South Carolina two male African-American Senators, the other being Republican Tim Scott.

–In Montana, Democratic Governor Steve Bullock has lost ground recently to Senator Steve Daines, watching his deficit increase from 1.8 points to 2.7 points post-conventions, while his likelihood of prevailing has dropped from 26.3% to 17.5%.

–In the regularly-scheduled Georgia Senate election, journalist Jon Ossoff continues to narrow the gap with Senator David Perdue, who continues to perform in racist and anti-Semitic ways, climbing from 2.6 points to 1.5 points down after the conventions. I estimate Ossoff now has a roughly 30% chance of winning, up slightly from 25%.

–In the open seat in Kansas, which has not elected a Democrat to the Senate since 1932, State Senator (and former Republican) Barbara Bollier is mounting a surprisingly strong challenge to House Member Roger Marshall. Prior to the conventions, she had already narrowed the “expected” deficit from 16.2 points to 3.6 points. Since the conventions, she trails by only 0.7 points, giving her a 38% chance to win.

Assuming the outcomes in these four races are unrelated to each other—a poor assumption, to be sure—Democrats have a 70% chance of winning at least one of these races, with Georgia and Kansas being the most likely.

Likely Republican (3). Democrats—and one Independent—are at least making life uncomfortable for three Republican Senators seeking reelection: Dan Sullivan of Alaska, Cindy Hyde-Smith of Mississippi, and John Cornyn (Senate Majority Whip) of Texas. Orthopedic surgeon Gross has closed the gap against Sullivan from 6.0 to 3.7 points, though that still gives him only a 1-in-9 chance of winning. First-term Senator Hyde-Smith again faces former Agriculture Secretary Mike Espy, who lost by “only” 7.2 points in 2018. Through August, Espy trailed by double digits, but a poll by the partisan-netural Tyson Group in late August had him trailing just 40-41 (with an astonishing 19% undecided or choosing a different candidate), which narrowed the deficit to around 8.7 points overall. The previous Tyson Group poll, conducted in March, had Espy trailing by 26 points! Finally, United States Air Force veteran Mary Jennings “M. J.” Hegar continues to chip away at Cornyn’s lead, climbing from 7.8 points to 5.8 points down. All this being said, I still expect Sullivan, Hyde-Smith and Cornyn to win with low-to-mid-single-digit margins.

Safe Republicans (10). Senators Bill Cassidy of Louisiana, Ben Sasse of Nebraska, Mike Rounds of South Dakota, Tom Cotton of Arkansas, James Risch of Idaho, Shelley Moore Capito of West Virginia and James Inhofe of Oklahoma should easily win reelection by double-digit margins. And in Tennessee and Wyoming, respectively, former United States Ambassador to Japan Bill Hagerty and former House Member Cynthia Lummis are expected to win by similar margins. Finally, while former United States Marine fighter pilot Amy McGrath has run a spirited race in Kentucky against Republican Senate Majority Leader Mitch McConnell, she is still likely to lose by around 10 points.

In sum, Democrats appear all but certain to net at least one Senate seat, losing in Alabama while winning in Arizona and Colorado, and are very well-positioned to win seats in Maine, North Carolina and, with less certainty, Iowa, giving them a narrow 51-49 majority; Warnock defeating Collins or Loeffler in January would increase that lead to 52-48. The question then becomes whether Democrats can add further seats in Georgia, Kansas, Montana or South Carolina…and even pull off an upset or two in Alaska, Mississippi or Texas.

Here is another way to think about these races.

An old “rule of thumb” says an incumbent polling below 50% is likely to lose, because undecided voters—who presumably know a great deal about the incumbent—will break against her/him. In reality, undecided voters tend to break in unpredictable ways, albeit generally in the same partisan direction in so-called “wave” years. Given the tens of millions of votes which will already have been cast by November 3, which then get factored into polling, this year’s undecided voters are even harder to predict—and may even break strongly in favor of Republicans, simply by virtue of not having voted early.

Table 2 lists candidate post-convention polling averages, prior to adjustment for partisan pollster bias, in the 15 most competitive Senate races, sorted by Democratic percentage:

Table 2: Post-conventions polling averages for Democratic and Republican 2020 Senate candidates

North CarolinaYes46.8%41.4%
South CarolinaYes44.8%46.2%
Georgia–LoefflerYes41.9% total44.6% total
MississippiYes41.0% in 2 Aug polls44.0% in 2 Aug polls

Kelly and Hickenlooper in Arizona and Colorado, respectively, are already at or above 50%, as is Tuberville in Alabama, suggesting these races are all but over. Incumbents Collins and Tillis, in Maine and North Carolina, respectively, are struggling to crack 42%, while Ernst in Iowa and Loeffler/Collins are well below 45%. For that matter, Marshall is struggling to reach 44% in Kansas, which leans 23.4 points Republican! With just over two weeks left, it is hard to see these incumbents make up that ground with voters, even if none of their Democratic opponents are polling much higher than 47%. Mississippi, meanwhile, is very difficult to gauge: in five polls taken between January and May, Hyde-Smith leads by an unweighted 52-36, but in the two August polls that deficit drops sharply to 44-41. This truly is the sleeper race.

Four other Republican incumbents are hovering around 46%–Graham, Perdue, Sullivan and Cornyn—which is in a kind of gray area between safe and in serious trouble. The good news for the latter two is that their opponents are struggling to top 42%. The bad news for Graham and Perdue is that their opponents are hovering around 45%–making undecided voters truly decisive in these two elections.

Peters in Michigan and Smith in Minnesota are hovering just below 48%, meanwhile, though they are still well ahead of their Republican opponents, who average around 40%. Daines in Montana, finally, is at 48.5%, close enough to 50% that Bullock may have a hard time catching him.

Bottom line: Democrats currently appear poised to pick up at least four seats, giving them a 51-49 majority. They are at least even money to win the Georgia special election and have at least modest opportunities to flip one or more of seven other Republican-held seats. If I simply sum the probabilities Democrats win each race, I get +5.1 using all polls and +6.0 using only post-conventions polls, though this is very “back of the envelope” methodology. Still, while Democrats could still net only one or two seats, a net gain of three-six seats is by far the likeliest outcome.

The strong likelihood of Democrats regaining control of the Senate is boosted by two historically-plausible scenarios:

  1. All polls are overestimating Democratic margins by 3.0 points.

In this scenario, Democrats remain strongly favored in Arizona (90.8%) and Colorado (97.3%) while headed for certain defeat in Alabama (0.0%), and they would be favored in Maine (74.0%) and North Carolina (75.5%), with Iowa essentially a toss-up (44.2%). Michigan would begin to get dicey as well, though Peters would still be an 89.0% favorite. Democrats would not be favored by more than 10% (Georgia special election) in any other race, though they would probably just net the three seats they need to regain control. The “back of the envelope” estimate is Democrats winning 2.9 seats, making control toss-up/Lean Democrat.

  • All polls are underestimating Democratic margins by 3.0 points.

While Alabama is still a near-lock to flip Republican, Democrats would be at least a 95.6% favorite to win Arizona, Colorado, Iowa, Maine and North Carolina for a minimum net gain of four seats. Democrats would also be 3-1 favorites in the Georgia special election, and the Senate races in South Carolina (51.0%), Georgia (61.9%), Montana (63.0%) and Kansas (64.7%) would be toss-ups, with Democrats likely to win at least two of them. They would also have a 35.2% chance of winning Alaska, and even a 13.6% chance of winning Texas. The “back of the envelope” estimate is Democrats netting 7.6 seats, making control a near-certainty, with a net 9-11 seats plausible, if still unlikely.


Very little has changed in the 11 states holding gubernatorial elections in 2020. Regardless of which polls you examine or what over- or under-estimation assumptions you make, Republicans are heavily favored to hold governor’s mansions in Vermont, New Hampshire, Indiana, Missouri, West Virginia, North Dakota and Utah. The closest margin is Missouri, where State Auditor Nicole Galloway trails Governor Mike Parson by an estimated 8.3 points. Similarly, Democrats are heavily favored to retain governor’s mansions in Delaware, Washington and North Carolina by double-digit margins, while Republican House Member Greg Gianforte is very likely to win back the Montana governor’s mansion—he leads Democratic Lieutenant Governor Mike Cooney by an estimated 7.4 points—for the first time in 16 years. Thus, Republicans will almost certainly net one governor’s mansion this year, increasing their edge to 27-23.

Until next time…please stay safe and healthy…

[1] That is, some variant of “If the election for United States House of Representatives was held today, would you vote for the Democrat or the Republican in your Congressional district?”

[2] Rhode Island, Illinois, Tennessee, Nebraska, South Dakota, Wyoming

3 thoughts on “October 2020 update: Democratic control of the Senate looks increasingly likely

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