Those worries intensified this week after the commission sent letters to 50 states and the District on Wednesday asking for a trove of information, including names, dates of birth, voting histories and, if possible, party identifications. The letters also asked for evidence of voter fraud, convictions for election-related crimes and recommendations for preventing voter intimidation — all within 16 days.
While the Trump administration has said it is just requesting public information, the letters met with swift — and sometimes defiant — rejection. By Friday, 25 states were partially or entirely refusing to provide the requested information; some said state laws prohibit releasing certain details about voters, while others refused to provide any information because of the commission's makeup and backstory.
"This entire commission is based on the specious and false notion that there was widespread voter fraud last November," Virginia Gov. Terry McAuliffe (D) said in a statement. "At best this commission was set up as a pretext to validate Donald Trump's alternative election facts, and at worst is a tool to commit large-scale voter suppression."
California, a state Trump singled out for "serious voter fraud," also refused to participate. Alex Padilla, the California secretary of state, said providing data "would only serve to legitimize the false and already debunked claims of massive voter fraud."
On Saturday morning, with news stories circulating about officials unable or unwilling to hand over all the requested data, Trump lashed out at them for "refusing to give information to the very distinguished VOTER FRAUD PANEL." He also suggested these states may have nefarious purposes for refusing to participate.
"What are they trying to hide?" he asked in a statement on Twitter.
Vice President Pence, who is chairman of the commission, hosted a conference call with the group's members Wednesday morning, three weeks before they are scheduled to have their first meeting in Washington. During the call, Kansas Secretary of State Kris Kobach (R), the vice chairman, told the other members about the letters.
A spokesman for Pence defended the letters, noting they seek information that is available publicly under state laws.
"The commission very clearly is requesting publicly available data in accordance with each state's laws in an effort to increase the integrity of our election system," Jarrod Agen, the spokesman, said in a statement. "The commission's goal is to protect and preserve the principle of one person, one vote because the integrity of the vote is the foundation of our democracy."
The request for records drew a new round of scrutiny to Kobach, a candidate for governor of Kansas in 2018 and an intellectual and political leader among conservatives who want to crack down on illegal immigration and the perceived threat of voter fraud.
In 2009, announcing his first bid for secretary of state, Kobach said that registration fraud by the defunct community organizing group ACORN made Americans wonder whether "the next election's going to be stolen." In office, Kobach aggressively pursued cases of potential fraud and promoted the "Crosscheck" system to see whether voters had registered in multiple states. But he frequently lost in court, as judges warned that measures meant to keep noncitizens off the rolls were ensnaring too many legitimate voters.
"It looks like they're putting together a database of who people voted for," said Jason Kander, a former Missouri secretary of state who runs the nonprofit group Let America Vote. "Democrat, Republican, independent, everybody should be outraged by that. "
The idea of collecting all national voter data for an audit has traveled through conservative circles for years. True the Vote, a group that promoted the fear that bogus voter registrations led to stolen votes in the 2008 election, also advanced the theory that millions of illegal votes denied Trump a popular mandate.
True the Vote itself has struggled to keep up momentum from the Obama era. Catherine Engelbrecht, the group's president, told supporters in a video message last week that True the Vote was not getting the donations necessary to meet its ambitions. The dream of a grass-roots national voter audit was simply not going to happen.
"We have gathered 2016 voter rolls; we've gathered information from thousands of resources," Engelbrecht said. "For us, it's never been about the headlines, or the promised presidential commissions, or the make-believe Russian hackers."
Two Democratic members of the commission said in interviews Friday that they were surprised by the backlash to the requests this week.
"We didn't think there'd be this heartburn over it," said Arkansas lobbyist David Dunn. "We were asking for information that, in most states, is considered public."
In West Virginia, Wood County Clerk Mark Rhodes said that he is confused by the angry reaction from some states.
"The request that went out is asking for public information, not any confidential information," he said. "If you want to make a match, you want to make sure you have enough data to avoid a false positive. In previous data matches, you might be Mark D. Rhodes on your driver's license and Mark Douglas Rhodes on your voter registration, and you've got a problem."
Experts described the request as unprecedented in scope, a recipe for potential voter suppression and troubling for the privacy issues it raises.
"This is an attempt on a grand scale to purport to match voter rolls with other information in an apparent effort to try and show that the voter rolls are inaccurate and use that as a pretext to pass legislation that will make it harder for people to register to vote," said Rick Hasen, an election-law expert at the University of California at Irvine.
Kobach's office did not respond to requests for comment; other members defended the letters.
"You meet people who say: I don't want to vote, because my vote doesn't count," said Dunn, the Arkansas lobbyist. "This commission has been broad-brush painted — and maybe rightly so — as some kind of voter suppression. But I don't feel like that's what I'm part of."
On Friday, as states said they would not participate, White House deputy White House press secretary Sarah Huckabee Sanders called that pushback a "political stunt."
Jenna Johnson and Christopher Ingraham contributed to this report.