Washington (CNN) President Donald Trump has called for a "major investigation" into his baseless claims that millions of illegal votes were cast -- but Democrats fear it will morph into new efforts to limit voting access.

Key party figures are gearing up to fight what they worry will be a spate of restrictive new election laws in GOP-controlled states -- largely enacted in reaction to fears that the White House is fanning.

Trump's claims of 3 to 5 million illegal votes are "a dog-whistle for Republican legislators who are looking for the go-ahead to enact restrictive voting laws to make it harder for people to vote," said Marc Elias, Democrats' top elections lawyer.

Priorities USA, the largest Democratic super PAC and a key Clinton backer in 2016, is aiming to turn its nonprofit arm into the party's major hub to fight for voting access.

Elias, who was the Hillary Clinton campaign's attorney, is joining the Priorities USA board of directors and the organization is absorbing Every Citizen Counts, which spent $17 million in 2016 on Elias-led legal challenges to what it saw as restrictive voting laws in North Carolina, Wisconsin, Ohio and Virginia.

In addition to backing Elias's efforts, Priorities USA is also building a national database that's intended to serve as a one-stop inventory of restrictive voting measures which will be shared with other progressive organizations. And it plans to launch social advocacy campaigns around its efforts to fight those measures. The group soon plans to bring on more staff to support the effort.

"We need to take a clear and aggressive stand that we're going to do everything we can," said Guy Cecil, the Priorities USA chairman.

Trump hasn't provided any evidence to support his claims of massive voter fraud, and Elias said he sees the White House's actions as motivated by Trump's ego, rather than genuine concern about voter fraud.

"It just shows how desperate he is to avoid looking like he got fewer votes than Hillary Clinton in the election," he said. "There were not millions of illegal votes. No one genuinely believes there were millions of illegal votes. And the President of the United States should be ashamed of himself for making this up."

Elias added: "It shows how clownish he can be around these issues where he's thin-skinned."

Trump vows to 'strengthen up voting procedures'

His comments came after Trump's White House said it plans to launch an investigation into voter fraud.

"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!" Trump wrote in two consecutive tweets Wednesday morning.

I will be asking for a major investigation into VOTER FRAUD, including those registered to vote in two states, those who are illegal and.... — Donald J. Trump (@realDonaldTrump) January 25, 2017

even, those registered to vote who are dead (and many for a long time). Depending on results, we will strengthen up voting procedures! — Donald J. Trump (@realDonaldTrump) January 25, 2017

Such an investigation would be "completely unprecedented," one Justice Department official said, because there is no specific, credible allegation of voter fraud for the department to investigate. So far, officials say there is zero evidence to support Trump's claim that 3 to 5 million people voted illegally.

A 2012 Pew Center study found that the American voting system was in need of an upgrade, with millions of invalid registrations and dead people listed on the rolls. But the study did not find fraud.

White House press secretary Sean Spicer said the investigation would focus on states where Trump did not compete, but did not say why the investigation would not also include states where Clinton did not compete.

And the White House has offered no evidence to support Trump's claims -- repeated in a meeting with congressional leaders this week -- that 3 to 5 million people voted illegally.

Other forms of manipulation

Democrats said they have seen this playbook before.

Cecil recalled working on Mark Pryor's Senate race in Arkansas in 2002. He said GOP officials stood outside polling places, took photos of voters as they arrived and asked to see their IDs.

"This is a new version of that," he said. "This is just the institutionalizing of voter suppression in a way we haven't seen in some time."

State elections officials have said Trump is right that some voter registrations are out of date. People die and people relocate -- and due to bureaucratic backups, some counties are slow to remove those former residents from their voter rolls.

But both Democrats and Republicans argue there are actually very few instances of voter fraud in which people cast multiple ballots, vote in someone else's name or vote despite being ineligible.

Even Trump's own legal team -- citing Elias and then-President Barack Obama's White House -- argued while objecting to Jill Stein's recount push that there was no evidence of voter fraud

"All available evidence suggests that the 2016 general election was not tainted by fraud or mistake," Trump's lawyers wrote.

But while cases of voter fraud are few and far between, judges have identified examples of systemic efforts to distort the voter rolls in recent years.

But those efforts voter suppression efforts hurt traditionally Democratic voters and help Republicans.

Some Democrats have said those efforts were a clear indication of voter fraud.

In North Carolina, a federal appeals court wrote in 2016 that -- after receiving data on the use of voting practices by race -- the Republican-controlled state legislature enacted a series of laws designed to suppress African-American turnout with " almost surgical precision ."

The state required voters to present forms of identification disproportionately used by white people. It cut back on early voting, limited same-day voter registration and preregistration for voters under 18, and it eliminated Sunday voting -- with the state even arguing in court that "counties with Sunday voting in 2014 were disproportionately black" and "disproportionately Democratic."

US Circuit Judge Diana Motz wrote in that the laws were "enacted with racially discriminatory intent."

"The General Assembly enacted them in the immediate aftermath of unprecedented African-American voter participation in a state with a troubled racial history and racially polarized voting," Motz wrote.

Democrats also believe that new voter ID laws played a role in lowering turnout in other states -- particularly Wisconsin, where Clinton narrowly lost to Trump. Turnout there dropped nearly 4 points from 2012, despite record early voting numbers.

Democrats are already preparing for fights in more states.

One possibility is Texas, where the Obama administration's Justice Department had led a challenge to the state's voter ID law, but Trump's administration has sought a pause in that case.

It's possible Priorities USA will need to find a plaintiff to continue that case if Trump's Justice Department drops its objection to the Texas law.

"I wish I could say that we are running out of states that were enacting bad voting laws to challenge. Unfortunately, a tremendous amount of damage has already been done to the ability to vote in this country by irresponsible legislative action before Trump took office," Elias said. "I suspect that that now will accelerate."