Joe Biden on Thursday night warned donors that President Trump will try to “indirectly steal” the 2020 election by making a case against mail-in ballots, a voting method that many are expected to use to avoid exposure to the coronavirus during November’s election.

The presumptive Democratic presidential nominee asked donors attending a virtual event to spread the word that “this president is going to try to indirectly steal the election by arguing that mail-in ballots don’t work.”

Trump will present mail-in ballots as fraud by making the argument that “they’re not real, they’re not fair,” Biden said.

During an appearance in June on “The Daily Show With Trevor Noah,” Biden had previously warned that Trump might “try to steal” the election. He has also said that Trump might try to delay the election and that the president might not leave the White House voluntarily if he does lose.

Biden’s remarks on Thursday offered the most detail about how he believes Trump might unfairly influence the outcome of the presidential contest. Biden’s campaign has mounted an aggressive voter-access effort, including hiring a team of lawyers to challenge any irregularities.