U.S. Rep. Bob Brady (D., Pa.) has a message for President Trump: Prove it.

The Philadelphia Democrat has asked officials in all 50 states and the District of Columbia to provide any evidence of voter fraud that might support the president's unsubstantiated claims that millions voted illegally in November's election, costing him the popular vote.

Brady, the top Democrat on the Committee on House Administration, sent letters to those officials Wednesday morning along with two senior Democrats, Reps. Elijah Cummings (D., Md.) and James Clyburn (D., S.C.).

"President Trump's outrageous claim that millions of people have voted illegally is unconscionably dangerous to the future of our democracy. He has no proof for his assertions but eligible voters all across the country will suffer as a result," Brady said in a news release.

The letters went to the attorneys general and top election officials in all 50 states. They ask for "a list of all specific cases in which either of your offices has determined that an individual who cast a vote in the federal elections held in November 2016 was legally prohibited from doing so." It seeks the person's name, the date of the prohibited vote, the polling place, the reason that person was barred from voting and the result of any prosecution that followed. The information was requested by Feb. 22.

Trump has repeatedly, and without evidence, alleged that massive voter fraud cost him the popular vote, which he lost by 3 million votes to Democrat Hillary Clinton. He reiterated the claim Monday night at a meeting with Congressional leaders -- making an allegation that casts a shadow over the integrity of U.S. elections and their results.

Democrats have painted his comments as a threat that could undermine U.S. democracy, while Republicans have either demurred or urged Trump to move on.

"I haven't seen evidence to that effect," Sen. John Thune (R., S.D.) said in Philadelphia Wednesday when asked about the fraud allegations. Speaking to reporters at the start of a Republican Congressional retreat, he said there are always voting irregularities, but wasn't sure about the scale of it. "I view the election as history and we're ready to roll up our sleeves and go to work."

The president, though, still appears fixated on the November results. On Wednesday morning Trump Tweeted that he "will be asking for a major investigation into VOTER FRAUD."

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