Then present for us proof that he has no evidence to show.
That's a reversal of the burden of proof.
The absence of evidence in this case is the evidence of absence.
When asked for evidence of election fraud, Mr Trump has failed on every single occasion to provide any substantiated evidence.
He's provided lots of claims and assertions.
He's provided lots of insinuations and criticisms.
What he has not done is provide ANY evidence.
Zip. Nada. Nothing. Zilch. Zero.
He's the head of the US government. All of the resources of the Executive Branch are at his disposal. The nation's intelligence agencies are at his beck and call. He has dozens of Republican state governors and Republican-led state legislatures doing his bidding. There are election-denial conspiracy theories, right-wing NGOs, think tanks and conservative PACs who would LEAP to do his bidding.
Yet, he's totally failed to substantiate his claims.
The 2017-2018 Presidential Advisory Commission on Election Integrity was disbanded without issuing a report (because it would have had to share its findings with Democrat members of Congress. It made no findings of fraud after 11 months of work.
The subsequent investigations under the Department of Homeland Security also failed to any significant voter fraud.
The DoJ has not made any significant investigations or prosecutions regarding widespread or statistically significant voter fraud. None of the politically appointed US Attorneys has launched any such action. Only individual prosecutions, numbering less than a few dozen.
Not assumption: proof. Or is not showing evidence only allowed for detractors of Trump? The only other proof that he is lying would be if there is there is knowledge that there is no election fraud in California.
What we've got here is a sick old man who's been making the same claim for nearly 2 decades and can't stop saying it because of the cognitive dissonance it would produce for him. He's trapped in a prison of a reality he's invented, and the real world is (as ever) stubbornly refusing to bend to his will.