The Trump campaign has also taken legal action in an attempt to halt vote counts in several battleground states, including Michigan and Pennsylvania, so that campaign observers can watch the ballots being opened and counted. Trump supporters have gathered in both states, calling to "stop the count."
Trump has said, baselessly, that he would win the election if only the "legal" votes were counted and the "illegal" were not, and he has suggested that the lead he held in key states on election night was subverted by "magical" dumps of ballots, which he tried to cast as late-arriving and, most importantly, suspect.
In 21 states, the law permits mail-in votes received after Election Day to be counted toward the final tally, according to data from the National Council of State Legislatures. They include three battlegrounds where ABC News has yet to project a winner: Nevada, Pennsylvania and North Carolina. In most of the states that allow late counting, absentee ballots must be postmarked by Election Day.
The president's comments have sparked "Count the Vote" protest marches across the country, and political leaders, including Sen. Elizabeth Warren, D-Mass., have called his rhetoric "undemocratic."
But this isn't the first time that Trump has demanded an end to voting counts.
2018 Florida midterms
Two years ago, during midterm elections, the gubernatorial and Senate races in Florida both fell within a 0.5% margin -- automatically triggering a recount.
Results showed Republicans slightly ahead in both races. In the Senate race, former Florida Gov. Rick Scott led incumbent Democratic Sen. Bill Nelson by a 0.15% margin, while in the race for governor, GOP Rep. Ron DeSantis led Democrat Andrew Gillum by a 0.41% margin. Gillum even walked back a concession, replacing it with "an unapologetic and uncompromised call to count every vote."
With the tallying underway, the president claimed, without citing evidence, that Democrats were engaged in voter fraud, rhetoric that mirrors almost exactly Trump's claims in the 2020 general election.
"All of a sudden, they're finding votes out of nowhere," the president said. "I say this: [Gov. Scott] easily won, but every hour, it seems to be going down. I think that people have to look at it very, very cautiously."
He took to Twitter to falsely claim that ballots in Florida's Senate and governor's race were "massively infected" and demanded an end to recounts and that both Republican candidates be declared the winners of their respective races.
Then-Florida Attorney General Pam Bondi also called for an investigation into any possible election misconduct. The Florida Department of State requested a federal investigation into altered voter forms, which voters who use mail ballots use to correct problems with signatures accompanying their ballots.
Ultimately, the votes were recounted, and the Republican candidates went on to win. An 18-month investigation by the Florida Department of Law Enforcement found no evidence of fraud with altered voting forms, Politico reported.
That wasn't the only election that year to elicit accusations of voter fraud and calls to stop vote counts. In Arizona, Democrat Kyrsten Sinema was in a close race against Republican Martha McSally for an open Senate seat left by outgoing Republican Sen. Jeff Flake.
Votes were still being counted in the days after the election, which is not uncommon, when Trump claimed without evidence that they were "all of a sudden" finding votes "out of the wilderness." Sinema had a slight lead at that point.
As tallying was underway in the competitive race, Arizona Republican leaders also sued, seeking an injunction to limit counts in urban counties that allowed voters more time to cure (or correct) mail-in ballots, the Associated Press reported. The counties in question were considered strongholds of support for Sinema.
Democratic leaders challenged the lawsuit, claiming it was an attempt to "silence thousands of Arizonans who already cast their ballots," while the GOP parties argued that they wanted consistency in counting votes.
The American Civil Liberties Union intervened in the case on behalf of the defendants, filing a brief that argued that "the court should not remedy the failure of some Arizona counties to provide voters with due process by prohibiting all Arizona counties from doing so," the organization noted in a report on voting rights.
The lawsuit was settled, with rural counties given more time to verify ballots.
Six days after the election, McSally conceded, and Sinema won the race -- the first time in 30 years that a Democrat won a Senate seat in the state.
Fast-forward to the 2020 presidential election, and Trump is repeating allegations of voter fraud and calls to stop vote counts.
"STOP THE COUNT!" he tweeted Thursday morning.
"ANY VOTE THAT CAME IN AFTER ELECTION DAY WILL NOT BE COUNTED," he added shortly after, prompting Twitter to flag the message as potentially misleading.
The Trump campaign later amended the message to be that all "legal" votes should be counted while those that are "illegal" should not (as opposed to merely stopping the count because he was ahead on election night and ballots counted later started to change that).
"We believe the American people deserve to have full transparency into all vote counting and election certification, and that this is no longer about any single election," the campaign said in a statement Friday. "This is about the integrity of our entire election process."
In return, former Vice President Joe Biden has urged Americans to "stay calm."
"Each ballot must be counted, and that's what we're going to see going through now, and that's how it should be," the Democratic presidential candidate said Thursday.
Several of the Trump campaign's legal attempts have been rejected, with judges in Michigan and Pennsylvania denying injunctions to halt vote counting.