On November 3, 2020, the presidential election between incumbent Republican Donald J. Trump and his Democratic challenger, former Vice President Joseph R. Biden, Jr., will mark the end of a weeks-long electoral process. Three months ago, I analyzed all publicly-available polls of the presidential election—nationally and by state, recognizing presidential elections are determined by the Electoral College—conducted since January 1, 2019.
Now the elections end in three months. As we wait for Biden to announce his vice-presidential running mate and the start of the Democratic National Convention on August 17, here is an update.
Table 1 lists the number of national polls assessing Biden vs. Trump conducted in 2019 and in each month in 2020. Sixty pollsters, with an average FiveThirtyEight pollster rating of B-, have assessed the 2020 presidential election at least once since January 1, 2019; only 38 have assessed the election more than once (mean B-).
Table 1: Number of 2020 Monthly National Polls Assessing Biden vs. Trump
|All of 2019||106|
Just eight pollsters (average pollster rating: B-) account for 53% of these polls, as well as 51% of the 281 polls conducted in 2020:
- YouGov (B-), 55 polls (40 in 2020)
- Morning Consult (B/C), 36 polls (31 in 2020)
- Ipsos (B-), 30 polls (23 in 2020)
- HarrisX (C), 21 polls (12 in 2020)
- Emerson College (B+), 18 polls (6 in 2020)
- Fox News (A-), 16 polls (7 in 2020)
- Optimus (B/C), 14 polls (13 in 2020)
- Change Research (C-), 14 polls (11 in 2020)
Figure 1 shows how Biden has fared monthly against Trump in 2020, using my weighted-adjusted polling averages (WAPA). I use pollster rating data to adjust for partisan lean (tendency to err more Democratic or Republican than other pollsters in analogous races) and quality. I weight more recent polls higher, using this ratio: number of days since January 1, 2019 divided by 673, the number of days between January 1, 2019 and November 3, 2020. I then average two versions of WAPA: one treating polls by the same pollster as statistically independent, and one treating all polls by the same pollster as a single, time-weighted value; differences between estimates are negligible.
Figure 1: 2020 Monthly weighted-adjusted average margins for Biden vs. Trump
Using all polls conducted since January 1, 2019, Biden leads Trump nationally by 7.2 percentage points (“points”). Biden’s margin rose from just over four percentage points in January and February, when he was fighting for the 2020 Democratic presidential nomination, to just under six points in the three months after Biden’s decisive win in the 2020 South Carolina Democratic presidential primary, to nearly nine points in June and July. The latter averages track closer to the FiveThirtyEight national polling average.
Again, though, presidential elections are fought across 50 states and the District of Columbia (“DC”), with the plurality winner in each state/DC winning every electoral vote (“EV”) from that state. Table 2 lists the number of polls within each state assessing Biden vs. Trump since January 1, 2019, plus that state’s 3W-RDM, my estimate of much more or less Democratic than the nation a state tends to vote; 10 states and DC have not been polled.
Table 2: Number of state-level polls assessing Biden vs. Trump since January 1, 2019
Fourteen states have been polled at least 10 times since January 1, 2019, of which 10 have been polled at least 10 times in 2020. Four of the top five, along with suddenly-swing North Carolina, are the closest states won by Trump in 2016: Michigan, Wisconsin, Pennsylvania, Florida. Four other Republican-leaning states have been frequently polled: Arizona, Georgia, Texas and Ohio, reflecting their status as ongoing or emerging battlegrounds. California, with 54 EV, rounds out the top 10.
National averages still matter, though. Combined with 3W-RDM, they provide the “expected Democratic-minus-Republican margin” in each state in 2020, all else being equal. Comparing polling averages to this expected value tells us where Biden may currently be under- or over-performing.
For example, Biden currently leads Trump nationally by 7.2 points. North Carolina has recently been 6.0 points less Democratic than the nation as a whole. Adding those two values together (7.2 – 6.0 = +1.2) suggests Biden could easily win North Carolina in 2020. Indeed, Biden leads Trump by an adjusted mean of 1.9 points in 52 polls conducted in North Carolina, implying Biden is “outperforming” expectations there by about 0.7 points. Table 3 lists every state’s expected value and WAPA.
Table 3: Expected and actual polling margins for Biden over Trump in each state in November 2020
* Only for the 40 states with both measures
The correlation between the expected margin and WAPA is +0.993, meaning polling matches expectations nearly perfectly—as one increases or decreases, so does the other. Still, Biden is polling ahead of those fundamentals by an average of about one percentage point, meaning state-level polling as a whole is even better for Biden than his excellent national polling; that said, the difference vanishes once you adjust for a state’s 2016 presidential election turnout.
Biden is underperforming expectations in some states, most notably woefully-under-polled Nevada. Biden leads there by 3.5 points, nearly six points lower than the 9.2 points by which he “should” be leading. Biden is also underperforming expectations in Iowa (-4.5) and Wisconsin (-3.9). By the same token, Biden is strongly overperforming in the traditionally Republican states of Arkansas, Utah, Oklahoma, Alaska, Texas and Arizona, as well as in reliably-Democratic Washington; the first four have only been polled 14 times in total, however. There is a partisan split in Biden’s over-and under-performance: in states with 3W-RDM>-5.0, Biden is underperforming by 1.7 points, on average. In states with 3W-RDM≤5.0, Biden is overperforming by 3.7 points. Many grains of salt are in order here, though. In recent elections, “fundamentals” have missed the final margin by an absolute value average of 5.4 points.
Still, the near-perfect correlation between the two values allows us to combine them into a single estimate of Biden’s margin over Trump on November 3, 2020, assuming polls become more predictive as an election gets closer:
- Assign expected value and WAPA equal weight as of January 1, 2020.
- WAPA weight increases, by day, with proximity to November 3, 2020.
I also calculated how likely Biden is to win the EV from each state, assuming this likelihood is distributed normally:
- For expected margins, I use mean = -0.8 and standard error = 7.1
- For WAPA, I use standard error = 3.0, roughly the margin of error in most quality polls; this is likely an over-estimate, as pooling reduces the standard error of the resulting polling average.
- Combined probability Biden wins a state’s EV calculated the same as for predicted final margin
While the means and standard errors I use are arguably arbitrary, albeit defensible, the final EV probabilities shown in Table 4 are in line with what other forecasters are saying.
Table 4: Estimated final state margins and probability of winning EV, Biden vs. Trump, November 2020
Three months before Election Day 2020, and with every caveat about voting during a pandemic, Joe Biden is the prohibitive favorite to be elected the 46th president of the United States.
- He is at least an 86.9% favorite in enough states—and by margins of at least four points—to earn him 308 EV, or 307 depending on what happens in Maine, which, along with Nebraska, allocates two EV to the statewide winner and one each to the winner of its Congressional districts. Moreover, Biden could lose Florida (+4.0, 86.9%), Nevada (+5.2, 87.9%) and one EV in Maine and still win 272 EV, two more than he needs
- He is a 70-75% favorite to win in Arizona (+1.9) and North Carolina (+1.8), for an additional 26 EV, increasing Biden’s total to 333/334 EV.
- The 34 combined EV of Ohio (+0.7) and Georgia (-0.8) are essentially toss-ups, meaning Biden has a roughly 75% chance to win at least one of them, putting him somewhere between 349 and 352 EV, with a maximum of 368 EV (or 369 with one EV in Nebraska).
Plus, it might take only a sharp break by undecided voters and a modest polling error for Biden to win the 44 combined EV of Iowa (-1.3) and the ultimate prize—Texas (-3.1). Thus, while something in the low-to-mid 300’s appears the most likely EV total for Biden, 413 EV cannot be discounted.
Using the simplistic—perhaps even simple-minded—method of multiplying Biden’s probability of winning each state by its EV and summing yields a “projected” EV total of 347.1, essentially adding Michigan, Pennsylvania, Wisconsin, Florida, Arizona, North Carolina, and one of Ohio/Georgia to the states 2016 Democratic presidential nominee Hillary Clinton won.
Biden’s lead looks even more robust when you make either of two historically-valid assumptions:
Polls systematically overestimate Biden’s margins by 3.0 points.
In this scenario, Biden’s projected EV drops to 299.7, which is still 29.7 more than required. He would be favored at least 80% to win in enough states to win 239 EV, though he would also be favored by at least 63.8% in three states totaling 34 EV, putting him over the top. Thus, even if Biden “only” wins the national popular vote by 4.2, he would likely still prevail.
Polls systematically underestimate Biden’s margins by 3.0 points.
In this scenario, Biden’s projected EV are a landslide-level 387.0, 117 more than necessary. He would be favored at least 80% to win enough states to earn 352 EV, while being a 74.6% favorite in Georgia, for a total of 368 EV. He would also be a 64.6% favorite in Iowa, with Texas essentially a toss-up at 55.3%–and a projected Trump victory of just 0.1%! Based on only one poll, Biden would even have a 33.2% chance of winning Arkansas’ 6 EV, with an 18.4% chance of winning Missouri’s 10 EV and a 10.9% chance of winning Alaska’s 3 EV. The last presidential candidate to come close to 433 EV was Republican George H. W. Bush, who won 426 EV in 1988.
None of this is to say Biden is guaranteed to be the next president of the United States; even three months from Election Day, it would be monumentally foolish for me to conclude that. Indeed, there are worrisome signs this year’s elections will not be conducted as efficiently and transparently as they could be. In an election in which a record number of voters are expected to cast their ballots by mail, delays in mail delivery—allegedly orchestrated by a newly-confirmed Postmaster General—could leave millions of votes uncounted because they did not arrive by November 3. Moreover, while Biden’s national polling lead has consistently ranged between four and 10 points over the last 19 months, a late-recovering economy or a last-minute “October surprise” could upend that trajectory.
All that being said, however, unlike Clinton in 2016, Biden has a sufficiently-wide range of paths to 270 EV that I estimate he is at least a 90% favorite to be elected president of the United States on November 3, 2020—or whenever ballots are ultimately counted.
Until next time…please stay safe and healthy…
 Hawaii, Vermont, Rhode Island, Illinois, Oregon, Louisiana, Nebraska, South Dakota, Idaho, Wyoming
 The former value is the mean arithmetic difference between “expected” and actual D-R margins across 153 state-level contests in 2008, 2012 and 2016, while the latter value is the standard deviation of these values. I recognize this is not a standard error. However, using the value 13.6—the range of values covering 95% of all values divided by 1.96, the final EV projection changes by only 1.0.
6 thoughts on “Biden vs. Trump: The view from three months out”