Democratic Federal Election Commissioner Ellen Weintraub is asking President Trump to disclose evidence of his charges of voter fraud in New Hampshire in the 2016 presidential election.

In a letter Wednesday, Weintraub wrote for a second time to Mr. Trump about his allegation that “thousands of voters were bused from Massachusetts to New Hampshire to vote illegally.”

In January, Mr. Trump tweeted, “I will be asking for a major investigation into VOTER FRAUD, including those registered to vote in two states, those who are illegal and....even, those registered to vote who are dead (and many for a long time). Depending on results, we will strengthen up voting procedures!” He cited no evidence at that time or afterward. In February, he tapped Vice President Pence to investigate his claims.

Get Breaking News Delivered to Your Inbox

She told him in her letter that “your allegations are not properly a matter for a future investigation to take up, as you cannot have responsibly alleged this scheme without already having sufficient facts in hand to do so.” Weintraub said she had seen no bus expenses on any campaign finance filing and said it’s “important” for Mr. Trump to provide evidence, so that “the truth of what happened in New Hampshire” can be determined.

Weintraub concluded by reminding him that democracy depends on the people’s faith in elections.

“Your voter-fraud allegations run the risk of undermining that faith,” she wrote. “Facts matter, Mr. President. The American people deserve to see your evidence.”

An outside group, Cause of Action, has called for an FEC inspector general investigation into Weintraub’s actions. Asserting that voter fraud is outside of the FEC’s jurisdiction, the group argues that an earlier letter she wrote to the president on the same issue that she posted on the FEC’s website misuses government property and time.