A former top adviser to President Donald Trump said time is running out to provide evidence to support claims of election fraud.

On Saturday, the Associated Press and other media outlets said former Vice President Joe Biden had won enough electoral college votes to be the next president. Lawyers representing Trump’s re-election campaign have fired off a number of legal challenges to the results, none of which have resulted in votes being thrown out.

“Allegations are not enough, and everybody knows this,” said Mick Mulvaney, former acting White House chief of staff and director of the Office of Management and Budget, in an interview with Yahoo Finance Live. Lawyers “have to put up or shut up on the evidence for the lawsuits. You can’t go out on TV and say, ‘they’re stealing the election,’ and not back that up with facts.”

Suits have been filed in five states alleging various ballot and voting irregularities; several cases have been thrown out. On Monday, the Trump campaign filed suits to try to stop election officials from certifying results in Michigan and Pennsylvania, claiming fraud.

According to the latest ballot count, Biden was ahead by 47,525 votes in Pennsylvania and by 146,123 in Michigan, with 99% tallied in both states.

“There are small instances of voter fraud in elections,” said Mulvaney. “It’s in the single digits sometimes, but it doesn’t move elections typically to 30,000 or 40,000 people. The difficulty is that so many people voted by mail, and it’s hard to grasp how many votes are still out there remaining to be counted.”

In March, Trump replaced Mulvaney with Mark Meadows as White House chief of staff. Mulvaney, who recently participated in the Greenwich Economic Forum, is currently serving as the United States Special Envoy to Northern Ireland, and co-founded a hedge fund, Exegis Capital.

Trump has made numerous unsubstantiated claims about election fraud in a steady stream of tweets and public comments over the past week, including the following Tuesday morning:

That tweet was flagged by Twitter (see above), which has been slapping an advisory on many of Trump’s posts.

Senate Majority Leader Mitch McConnell said on the Senate floor Monday that Trump has “every right to look into allegations and request recounts.”

Mulvaney said Trump and McConnell’s adherence to procedure makes sense, and emphasized that it’s the states and the electoral college, not the media, who certify election winners. He said waiting for that certification doesn’t threaten faith in the system. “I think that’s hyperbole that the media has been pitching for a long time. I don’t think it undermines democracy in any way, shape or form.”

Waiting for the count to be completed and alleging fraud are two different approaches, however, and Mulvaney said of the latter, “you can’t continue that forever. Sooner or later, you have to admit that you won or lost.”

Julie Hyman is an anchor on Yahoo Finance Live, 9am-11am ET.

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