Joe Biden said he is concerned Donald Trump will try to delay the November presidential election.

“Mark my words, I think he is going to try to kick back the election somehow, come up with some rationale why it can’t be held,” Biden, the presumptive Democratic nominee, said on Thursday night in remarks at an online fundraiser.

Under the law, no president has the power to postpone the presidential election. To change the date, Congress has to intervene.

Trump has not announced plans to delay the 3 November election, but it is a concern both political parties have raised. The president has repeatedly demonstrated a lack of understanding about the limits on executive power, particularly when it comes to his own self-preservation.

The Covid-19 outbreak has also increased concerns about how to conduct in-person voting safely. In response, many are pushing for an expansion of voting by mail.

Trump has used Covid-19 press briefings to make false claims about voting by mail, calling it “corrupt” and “dangerous”. Earlier this month, Trump also urged Republicans to fight efforts to expand voting by mail.

“Republicans should fight very hard when it comes to state wide mail-in voting,” Trump tweeted. “Democrats are clamoring for it. Tremendous potential for voter fraud, and for whatever reason, doesn’t work out well for Republicans.”

At the fundraiser, Biden also referenced reporting by the Washington Post which revealed Trump’s reluctance to fund the US postal service and efforts to force changes to its financial structure, which could harm voting by mail.

“Imagine threatening not to fund the post office. Now, what in God’s name is that about? Other than trying to let the word out that he’s going to do all he can to make it very hard for people to vote,” Biden said. “That’s the only way he thinks he can possibly win.”

The Covid-19 outbreak has already reshaped the 2020 campaign. The candidates are campaigning from home and at a stage in the cycle when the election tends to dominate news coverage, reporters are instead focused on Covid-19.

Biden also shared a broader concern about interference in the presidential election by Russia and two unnamed “major actors”.

“I promise you the Russians did interfere in our [2016] election and I guarantee you they are doing it again with two other major actors,” Biden said. “You can be assured between [Trump] and the Russians there is going to be an attempt to interfere.”

In response to Biden’s comments, the Trump campaign said in a statement: “Those are the incoherent, conspiracy theory ramblings of a lost candidate who is out of touch with reality. Perhaps he also missed the news that the infamous Steele Dossier, central to the Russian Collusion Hoax, was likely compiled with Russian disinformation. That’s the real Russian collusion.”