There is no evidence of widespread voter fraud in U.S. elections, though Trump has spent years claiming there is and that it cost him the 2020 election he lost.

Instances of voter fraud do occur on occasion — like when people fill out a recently deceased relative’s ballot or lie on a mail ballot application — and they are usually caught. A tracker from the conservative Heritage Foundation has collected more than 1,600 incidents of voter fraud over 40 years, a tiny fraction of the total votes cast over that period.

Trump’s offer Monday is his latest to exert greater influence over the midterm elections. His administration has dedicated significant resources into searching for noncitizens on the states’ voter rolls. The Department of Justice sued California officials in an attempt to force them segregate mail ballots it says went to potential noncitizens. Noncitizen voting is also a rare occurence, studies show.

Last week, the DOJ sued Alaska officials, at Trump’s request, in an effort to prevent the results of the U.S. Senate race from being certified if GOP Sen. Dan Sullivan loses.

Courts have also blocked Trump from making sweeping changes to mail voting and requiring documentary proof of citizenship to vote.

Trump’s voter fraud reward announcement comes after he unveiled a $25 million government fraud whistleblower program, telling reporters he’d decide who was worthy of the prize.

He has also been making other financial promises as he hits the campaign trail for Republicans ahead of the midterms, including $5,000 payments to Americans if his party maintains control of Congress. Trump has similarly not clarified where the money would come for those payments.