What reason explains why Democrats are more likely to mail in their ballots?
10I don't have any evidence to back this up (which is why this isn't an answer), but I suspect "Trump said I shouldn't vote by mail" is probably a contributing factor.– Joe CNov 6, 2020 at 19:21
12They don't, in general, this election is a special case, driven largely by COVID-19 and Republican attacks on mail-in voting– divibisanNov 6, 2020 at 19:25
The question should be Why are Democrats more likely to vote by mail in some states than Republicans? Mr. Biden's early lead in Arizona is diminishing because Republicans have been voting by mail in that state for some time.– David HammenNov 6, 2020 at 20:26
Joe C: so is the COVID pandemic, the perceived severity of which tends to split along party lines. It is likely that Democrats were more inclined to avoid in person voting and opt for mail in out of fear of infection. I do not think very many people voted in person because trump told them to.– acpilotNov 7, 2020 at 19:55
I tracked down the following explanation in a Washington Post article:
Why do so many more Democrats than Republicans plan to vote by mail?
One clear explanation of the growing gap has been well documented: Partisans often take cues from their party’s elites, as scholarship has long found. When Trump criticizes voting by mail, as he frequently does, Republicans take note. When other Republican politicians reiterate Trump’s comments, the cue is made even more clear.
But we found another possible reason: Republicans and Democrats respond differently to information about the pandemic. When we showed respondents projections about how the pandemic would probably unfold, Democrats became more likely to want to vote by mail. Republicans did not.
Reading the projections had the biggest effect in April. As both the pandemic and the election campaigns unfolded, covid-19 projections mattered less. At the same time, the differences in Democrats’ and Republicans’ plans grew. This suggests that Americans’ opinions crystallized somewhat over the summer as those two groups’ views of the pandemic diverged.
That may be because Republicans are more likely to distrust experts than Democrats. Research conducted before the pandemic found that Republicans are less likely to view scientists as trustworthy sources of information. This appears to have spilled over into the issue of whether to vote by mail, contributing to the growing partisan gap.
Regardless of the reason, if Trump’s goal was to get more Republicans to vote in person, he will probably get his way in November. As a result, any hiccups in counting mail ballots would be most likely to hurt Democrats.