President Trump’s call for a nationwide investigation into voter fraud has brought cackles from the Left, but elections integrity organizations call it long overdue.

Trump tweeted Wednesday, “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!”

“I am incredibly optimistic that we may be able to finally tackle the very real problems plaguing our election processes.”

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Critics have ridiculed Trump’s unsubstantiated claims that millions of illegal voters cast ballots in the 2016 election. But advocates said documented cases of fraud prove the problem is real, if unquantified.

“I am incredibly optimistic that we may be able to finally tackle the very real problems plaguing our election processes,” True the Vote founder Catherine Engelbrecht said in a prepared statement. “The chaos documented during the 2016 election cycle was the clearest and loudest warning shot to date — systemic election problems must be resolved, or they will soon be the cause of a national crisis.”

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J. Christian Adams, president and general counsel for the Public Interest Legal Foundation, said in a prepared statement that America’s electoral system is in dire need of new safeguards.

“The Obama administration had the tools to fight voter fraud but let them gather dust,” he stated. “Because of that neglect of their duties, aliens got on the rolls, people voted multiple times, and lawlessness took hold of our elections.”

Han von Spakovsky, a former member of the Federal Election Commission who co-wrote a book on voter fraud in 2012, said it is impossible to estimate the extent of illegal voting because there are no systematic procedures to detect and prevent it.

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“The issue is we don’t know,” said von Spakovsky, who now is manager of the Election Law Reform Initiative at the Heritage Foundation. “We have an honor system across the country … We know that voter fraud occurs.”

Some high-profile cases have involved people who hold positions of authority:

Wendy Rosen, a Democratic candidate for Congress from Maryland, admitted to voting in Baltimore County in 2006 and 2010 even though her official residence was in Florida. A state judge sentenced her in 2013 to a probation and a fine.

Meloewese Richardson, a longtime poll worker in Ohio’s Hamilton County, admitted to voting twice in the 2012 election and voting three times — in 2008, 2011, and 2012 — in the name of her sister, who had been in a coma since 2003. She acknowledged wanting to help Barack Obama win. A state judge sentenced her in 2013 to five years in prison.

Idalia Lechuga-Tena, a Democratic state representative in New Mexico acknowledged in 2015 that she had voted before she became a naturalized citizen.

Public Interest Legal Foundation spokesman Logan Churchwell said in each of those cases — and many others involving ordinary people — the Department of Justice under Obama declined to file federal criminal charges.

Churchwell said the idea of a national investigation into election procedures should not be controversial. He noted that former President Jimmy Carter and former Secretary of State James Baker headed up an election commission in 2004, resulting in a number of recommendations, including that states adopt laws require voters to show identification at the polls.

Churchwell said Trump could — and should — order the Department of Homeland Security to share immigration records with states so they can cross-reference it with voter registration data to identify non-citizens on the rolls. Some states asked for that information — only to be told “no” by the Obama administration.

Without those records, Churchwell said, it is impossible to know how widespread illegal voting is.

“Only the federal government can answer that question,” he said.

Churchwell also said that election officials ought to refer illegally registered voters to law enforcement authorities rather than simply scrub them from the rolls.

Those and other steps would be “far better than what we currently have, which is that you say you’re a citizen when you register to vote and no one checks,” he said.

Von Spakofsky said a section of the “motor voter” law, formally called the National Voter Registration Act, allows the federal government to sue jurisdictions that fail to maintain accurate voter registration records. But he said the Obama administration instructed Justice Department lawyers not to enforce that provision.

That has left it to private advocacy groups like the Public Interest Legal Foundation to try to force elections officials to remove dead voters from the rolls. The law firm has sued jurisdictions across the country that have more registered voters than voting-eligible adults. On Wednesday, it announced an agreement negotiated with Noxubee County in Mississippi, where the number of registered voters were greater than 100 percent of voting-eligible citizens in the 2010, 2012, and 2014 elections.

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On Friday, the firm will go to federal court in Virginia seeking a court order compelling officials in Manassas to provide more information about registered voters. PILF found more than 1,000 non-citizens were registered to vote in eight jurisdictions that voluntarily shared data. Manassas and other jurisdictions denied the law firm’s request.

Ohio Secretary of State Jon Husted, responding to a question about a probe into voter fraud, told CNN that “more information’s always useful.” He said his state regularly conducts a review after each election; he said authorities found about a thousand case of voter irregularity.

“It exists. It’s rare,” he said. “We’re building a stronger system so that it doesn’t happen.”

Von Spakofsky said there is no reason for liberals to insist elections are error and fraud-free.

“It’s really odd,” he said. “I don’t understand why people on the Left want to say there’s no voter fraud.”