“Our election system has been stress-tested by three successful elections already this year,” said Jocelyn Benson, the Democratic secretary of state of Michigan. “We have protections in place to ensure election officials track and verify every ballot they send and receive, and in every instance we ensure that each person gets only one vote.”
Reid Magney, a spokesman for the nonpartisan Wisconsin Elections Commission, said that each absentee ballot cast in the state is processed by poll workers on Election Day and checked against poll books to make sure the voter has not already voted in person.
In California, some counties use traditional, neighborhood-based polling places and others use larger, more centralized vote centers. At traditional polling places, voters who receive a mail ballot must surrender it if they decide to vote in person instead. At vote centers, electronic poll books allow officials to check if a voter has cast a ballot elsewhere before permitting them to vote, according to a statement issued Thursday by Sam Mahood, a spokesman for the California secretary of state, Alex Padilla, a Democrat.
In New York City, Frederic M. Umane, a Republican who sits on the city’s Board of Elections, called its system to prevent double voting “fail safe.”
Votes in New York City are immediately uploaded to a central computer, Mr. Umane said. When a voter goes to sign in, if they already voted, the system would flag it. And before any mail-in vote is counted, a check is made to see if that person also voted either in early voting or on Election Day.
Mr. Umane said the city implemented a new electronic poll book system last November and ran a series of tests beforehand to make sure it worked, adding that he was not aware of Mr. Trump’s comments this week.
“I’m a Republican,” Mr. Umane said, “but I don’t necessarily listen to everything Trump says.”
Peter Baker contributed reporting.