President Trump warned that if states like Nevada are allowed to send mail-in ballots to all registered voters, it could take "years" to get the results from November's election.
In a wide-ranging interview with "Fox & Friends," Trump claimed that the infrastructure is not there for such a large-scale operation.
"It could be for months and months," Trump said about how long it may take for votes to be counted. "It could be for years."
The president pointed to a congressional primary election in New York that has resulted in weeks of vote counting after voters mailed in their ballots.
Trump's campaign and the Republican National Committee filed a lawsuit against Nevada on Tuesday, claiming that the state's expanded mail-in voting plan would expose the election to fraud.
"What they're going to do is blanket the state," Trump said Wednesday. "Everyone who ever walked is going to get one."
Republicans have expressed concern that this would result in ballots being sent to dead people, those who have moved, and others who are currently not eligible to vote.
Former Secretary of State Hillary Clinton has claimed that "Republican sabotage" of the U.S. Postal Service is part of Trump's strategy to stand in the way of mail-in voting. Trump said Clinton is "living in a cocoon" and still has not accepted the results of the 2016 election.
Trump did differentiate between sending ballots to all voters and allowing people to apply for absentee ballots.
"Absentee is OK because you have to go through a process," Trump said. On Tuesday, the president encouraged Florida voters to vote by mail, stating that the system there is both safe and secure.
"They have an infrastructure that’s taken years to build," Trump said about Florida's mail-in voting system.
Democrats are insisting that mail-in voting be made available so that people do not have to put themselves at risk of catching or spreading coronavirus at the polls. When asked what his administration will do to make in-person voting safer -- especially for at-risk senior citizens -- Trump expressed hope that the situation will be better by then.
"By the time we get there we'll probably be in very good shape," he said, stating that numbers are declining in states like Florida, California, and Texas. At the same time, Trump recognized that "you could have a second wave."
Addressing upcoming debates against Democrat Joe Biden, Trump said he is "ready to debate," but lamented that the first debate is scheduled for late September, after some ballots will already have been sent out to voters.
The president also indicated that Biden's team is "trying to get out" of the debates, although he acknowledged that Biden himself has never said this. Biden's campaign insists the candidate will be at the debates, despite the GOP speculation
Trump also said that Biden has been "totally taken in" by radical leftists, pointing to his Unity Task Force that he formed with Sen. Bernie Sanders, I-Vt.
Biden's wife Jill told Fox News on Tuesday that her husband is a moderate, not the far-left candidate Trump's campaign is making him out to be.
"Joe Biden is whatever they tell him to be," Trump said in response to this.
Fox News' Brie Stimson contributed to this report.