Donald Trump warned darkly of potential voter fraud at the first meeting of his election integrity commission on Wednesday, minutes after its chair, Mike Pence, insisted that the commission had “no preconceived notions”.

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Speaking to the commission, which comprises a mix of leading conservative advocates for more restrictive voting laws and state and local Democratic officials, Trump said of those state officials refusing to cooperate with the commission: “One has to wonder what are they worried about.” He added: “People would come up to me and expressed concern about voter inconsistencies and irregularities which they saw in some circumstances having to do with very large number of people.”

No state has fully cooperated with the commission’s expansive request for data, which includes the social security numbers of voters, though many have partially done so. State election officials have cited privacy concerns and statutory prohibitions in refusing to share all requested data with the commission. These officials include several members of the commission, among them its vice-chair, Kansas secretary of state Kris Kobach, who made the original request for voter data on behalf of the commission.

Trump has long insisted that he won the popular vote in the 2016 election but vast voter fraud was responsible for Hillary Clinton’s margin of almost three million votes over him. He tweeted in late November: “In addition to winning the Electoral College in a landslide, I won the popular vote if you deduct the millions of people who voted illegally.” There is no evidence for this statement and it met with bipartisan denunciation.

Kobach, who has long claimed there is significant voter fraud in American elections, later echoed Trump’s tweets in an interview with MSNBC’s Katy Tur, claiming “we may never know the answer” to which candidate won the popular vote in the 2016 election.

Pence first announced the commission, which was prompted by Trump’s unfounded claims of voter fraud in the 2016 election, in a private gathering with Republican members of Congress in January. Then, as first reported by the Guardian, the vice-president said the new administration would “initiate a full evaluation of voting rolls in the country and the overall integrity of our voting system in the wake of this past election”.

Democrats held multiple events to denounce the commission, which they have seen as a vehicle to promote voter suppression.

At the Democratic National Committee, Jason Kander, president of Let America Vote and former Missouri secretary of state, dubbed it “The Voter Suppression Committee to Re-Elect the President”.

He told reporters: “This commission started as a way to try and legitimize, to try and justify the biggest lie that a sitting president has ever told. But it has morphed from there and what it has become now is just a vehicle for voter suppression.”

Kander said he had seen the Republican voter suppression “playbook” up close. It aimed to undermine faith in American democracy so people believed drastic measures must be taken, put up obstacles to voting and put up obstacles beyond those obstacles. The strategy went back decades, he added.

The Missouri Democrat, who lost a 2016 Senate campaign, warned that the commission’s attempt to harvest voter data was already causing some people to cancel their registration, an immediate demonstration of voter suppression.

This was echoed by Alex Padilla, California’s secretary of state, at a panel discussion hosted by the liberal Center for American Progress on Wednesday. “The fundamental premise of the commission is to try to justify Donald Trump’s ego that he did not win the national popular vote because he can’t accept that fact,” he said. Padilla, who tangled with Trump on Twitter when the president claimed without evidence that there was “serious voter fraud” in California, said the commission’s strategy was to foment distrust in the US election system.

“If you get it into people’s mind that maybe their vote won’t count or maybe their vote won’t be counted, then [they think]: ‘Why should I bother to go vote?,’” Padilla said. “Turnout goes down. The vote is suppressed.”

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