“We are sounding an alarm and saying that this is a very real possibility, that the data is going to show on election night an incredible victory for Donald Trump,” Josh Mendelsohn, the chief executive of the group, Hawkfish, told “Axios on HBO.” The company’s survey of registered voters concluded that twice as many planned to cast a ballot by mail as ever before, and that they were mostly Biden supporters.
A spokeswoman for the Trump campaign, Thea McDonald, called Democrats’ concerns about the president prematurely declaring victory “an unsubstantiated conspiracy theory,” adding, “President Trump and his campaign are fighting for a free, fair, transparent election in which every valid ballot counts — once.”
As Mr. Trump demonizes mail ballots, many of his supporters do not plan to use them.
An NBC/Wall Street Journal national poll last month found that nearly half — 47 percent — of supporters of Mr. Biden planned to mail in their votes, compared with two-thirds of Trump supporters — 66 percent — who planned to vote in person on Election Day.
In some states, the discrepancy is even more stark. A recent Marquette Law School poll of Wisconsin, another swing state, found that among voters planning to cast a mail ballot, Mr. Biden was favored by 67 percentage points. Among those who planned to vote on Election Day, Mr. Trump led by 41 points.
Mr. Trump himself casts his own Florida ballots as an absentee voter. He has claimed a distinction between “good” absentee ballots and “bad” mail-in ballots, but there is no meaningful difference. His real target seems to be certain states — which this year include California, New Jersey and Utah — where all active registered voters are sent mail-in ballots, not just ballot request forms. Thirty-four states allow all voters to use an absentee ballot without an excuse, mailing it back or dropping it off.
Elections experts say that absentee or mail voting is potentially more subject to instances of fraud than in-person voting, but that states with a history of all-mail voting have a minuscule number of cases. Wide-scale cheating that could swing a close race would be easy to detect.