President Donald Trump's plans to ask for a "major investigation" into allegations of widespread voter fraud were met with skepticism by both Democratic and Republican lawmakers - and fear from voting rights advocates that the president will use his unfounded claims to justify more-restrictive voting laws.

It is unclear who will investigate Trump's belief that he lost the popular vote in November's election because millions of illegal votes were cast. The president could set up an independent commission or task force to look into the claims, which have already been disproved by many national studies. White House press secretary Sean Spicer said the president's investigation would examine "the integrity of our voting system" and not just the 2016 election.

The Justice Department, which investigates claims of election crimes, has not historically launched a criminal investigation at the request of a president. An attorney general could order an investigation, but Trump's nominee, Sen. Jeff Sessions, has not yet been confirmed, and his spokeswoman declined to comment. Justice officials said they knew nothing about an investigation into voter fraud and referred questions to the White House.

Former assistant attorney general for civil rights Tom Perez, who oversaw the department's voting section under former President Barack Obama's administration, called Trump's announcement of a voter fraud probe "a totally stupid and wasteful investigation into nonexistent problems."

"I can't think of a more colossal waste of taxpayer dollars than to initiate this investigation," said Perez, who was also labor secretary and is now a candidate for chair of the Democratic National Committee. "This is all about ego. The issue of in-person voting fraud is virtually nonexistent."

In back-to-back tweets on Wednesday, Trump said the investigation would cover "those registered to vote in two states, those who are illegal" and "those registered to vote who are dead (and many for a long time)."

News outlets reported Wednesday that Trump's daughter Tiffany, White House chief strategist Stephen Bannon and treasury secretary nominee Steven Mnuchin were all registered to vote in two states.

"Depending on results," Trump added in his tweet, "we will strengthen up voting procedures."

Former Justice spokesman Matthew Miller said this is exactly the fear of voting rights advocates - that such an investigation will be used to endorse more-restrictive voting laws. "That's where this is going," Miller said.

Civil rights groups are specifically worried about an action the Justice Department took three hours after Trump's inauguration on one of the most controversial voting laws in the country - a 2011 voter ID law in Texas, which every judge who has considered it has found to be discriminatory. On Friday, Justice officials asked for a months-long delay in a hearing in the case so they can determine their next course of action, which could include dropping out of the case altogether.

Trump called for the voter fraud investigation after insisting during a private reception with congressional leaders on Monday that there were between 3 million and 5 million ballots illegally cast in the election, allowing his Democratic rival Hillary Clinton to win the popular vote by more than 2.8 million votes. Clinton ultimately lost the electoral college vote to Trump.

House Speaker Paul Ryan, R-Wis., said he has "seen no evidence" to that effect, and Sen. Lindsey Graham, R-S.C., said that the president's allegations were undermining faith in the democratic system.

"I would urge the president to knock this off," Graham said. "This is the greatest democracy on Earth. We're the leader of the free world. And people are going to start doubting you as a person if you keep making accusations against our electoral system without justification."

Rep. Jason Chaffetz, R-Utah, chairman of the House Oversight and Government Reform Committee, said, "I don't see the evidence [of fraud], but he's the president, and if he thinks it's there, have at it."

Sen. Dianne Feinstein (Calif.), the ranking Democrat on the Senate Judiciary Committee, called Trump's claim "absolute nonsense," and House Minority Leader Nancy Pelosi, D-Calif., said she could not understand why the newly installed president is "so insecure."

Pelosi called Trump's focus on voter fraud "really strange" - especially because his own lawyers disputed allegations of ballot irregularities when Green Party presidential candidate Jill Stein challenged the results in some states last fall.

"All available evidence suggests that the 2016 general election was not tainted by fraud or mistake," Trump's lawyers stated in a recent court filing in that case.

"I frankly feel very sad for the president making this claim," Pelosi added. "I felt sorry for him. I even prayed for him - but then I prayed for the United States of America."

The organization that represents secretaries of state who run local elections said it is "not aware of any evidence that supports the voter fraud claims made by President Trump." Ohio's Republican Secretary of State Jon Husted questioned the need for a voter fraud investigation, saying that Ohio conducted a review four years ago and has another review of the 2016 election underway.

"Easy to vote, hard to cheat," Husted tweeted.

The president and his aides have yet to provide any verifiable facts to back up his claim, and analyses of the election found virtually no confirmed cases of voter fraud, let alone millions. While there have always been some isolated instances of alleged voter fraud, voting experts say there is no evidence of widespread fraud that affects elections.

"I think taking the necessary steps to study and to track what we can do to both understand this, the scope of the problem, and then, secondly, how to stop the problem going forward is something that's definitely, clearly in the best interest," Spicer said.

Spicer cited research that he said backs up Trump's claims. But Spicer cited a Pew study that does not support this claim. He also conflated the Pew study with another study that also does not support the voter fraud claim.

A 2012 Pew Center on the States study found problems with inaccurate voter registrations, people who registered in more than one state, which can happen if the voter moves and registers in the new state without notifying the other state, and deceased voters whose information was still on the voter rolls.

The primary author of the Pew report tweeted in response to the Trump staff's claim that he "can confirm that report made no findings re: voter fraud."