Trump repeated the unproven claim to congressional leaders on Monday, and his press secretary on Tuesday affirmed "the president does believe that." There is still no proof of widespread fraud.
The Trump transition team pointed to one heavily criticized study, as well as an analysis that didn't count fraud, as evidence that "millions of people" voted illegally.
"There are so many checks and balances on this system. It continues to prove itself on a daily basis," said Karen Osborne, the director of elections in Maricopa Country, Ariz.
Rick Hasen, founder of the Election Law Blog, discusses Donald Trump's claims of potential voter fraud. "He's threatening the bedrock of democracy, and doing it to claim he's not a loser," Hasen says.
In tight elections, the loser often calls for a recount. But recounting ballots might not be easy in states that use paperless machines — including the presidential battleground state of Pennsylvania.
For as long as tales of voter fraud have had currency among conservatives, the notion of liberal media bias has been an article of faith for even longer. The combination has become central for Trump.
Donald Trump is calling on Pennsylvania voters to also monitor polling places for fraud. The effort has prompted fears for the integrity of the electoral process.
The stage appears to be set for many Americans to question the legitimacy of this year's election results. The consequences of that are unknowable and potentially dangerous.
The state requires its residents to prove their citizenship when registering to vote, but a federal agency fought the law in court. It now appears to have changed positions.