President Donald Trump said Wednesday that he will launch a major federal investigation to determine the pervasiveness of voter fraud in the United States.

'You have people that are registered who are dead, who are illegals ... You have people registered in two states. They're registered in a New York and a New Jersey. They vote twice,' Trump told ABC News.

'There are millions of votes, in my opinion. Now we're going to do an investigation.'

'I want the voting process to be legitimate,' Trump said during an Oval Office interview, while insisting that no one committed voter fraud to help him win the White House.

'Of those votes cast [illegally], none of them come to me. None of them come to me,' he said. 'They would all be for the other side.'

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President Donald Trump said Wednesday that many illegal immigrants are registered to vote, others are registered in more than one state, and voter rolls are flush with dead people in whose names ballots are sometimes cast

Trump said Wednesday morning that he will launch a major investigation into voter fraud, doubling down on a belief that drew widespread head-shaking on Tuesday – the idea that millions cast ballots illegally in November

The move to probe the nation's voting systems, which Trump first announced on his Twitter feed, came less than 24 hours after White House press secretary Sean Spicer defended Trump's oft-repeated claim that millions of people cast ballots illegally in November.

'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)' the president wrote in a pair of tweets.

'Depending on results, we will strengthen up voting procedures!'

Spicer found himself behind the 8-ball on Tuesday as reporter after reporter challenged him for evidence, ultimately blurting out that the Trump administration might launch an investigation into the possibility.

'Maybe we will,' he told one journalist during his daily press briefing.

Pressed on what that could mean, a flustered Spicer insisted that he 'did not' leave the door open for a wide-ranging government probe – but then allowed that 'anything is possible.'

Rather than run from an issue that led reporters and pundits to call him a liar, Trump doubled down and outlined the rationale for a federal probe

White House press secretary Sean Spicer told reporters on Tuesday that 'maybe we will' investigate Trump's belief in millions of illegal votes, allowing that 'anything is possible'

By Tuesday night, White House officials were pondering what to do. One told DailyMail.com after dinnertime that a quick decision had been reached to seize the opportunity the topsy-turvy news cycle had provided – and make lemons into lemonade.

'There are people voting illegally,' the official said. 'Let's find out how many.'

The president told a group of Republican and Democratic lawmakers Monday night that he would have won the popular vote if it weren't for between 3 and 5 million illegal votes, according to people who were present.

'He was having a discussion with some folks and mentioned something in passing,' Spicer told reporters on Tuesday.

Trump told ABC Wednesday that the 'conversation lasted like a minute - it was hardly even discussed.'

But he admitted: 'I said it, and I said it strongly.'

Democratic nominee Hillary Clinton collected nearly 3 million more votes than Trump but lost decisively in the Electoral College because the largest part of her popular-vote advantage was concentrated in a small number of states with giant Democratic voter bases.

As disenchanted Democrats argued against the merits of the Electoral College system in the wake of his victory, Trump tweeted that '[i] n addition to winning the Electoral College in a landslide, I won the popular vote if you deduct the millions of people who voted illegally.'

He also claimed on Twitter that there was 'serious voter fraud in Virginia, New Hampshire and California,' and challenged the media to report on it.

Spicer punted a question on Tuesday asking for specific evidence of voter fraud in November, rather than a statistical probability that it happened.

Trump told congressional leaders Monday night that he would have won the popular vote if millions of illegal immigrants hadn't fraudulently voted for Hillary Clinton

NPR reported in late November that the Trump transition team had provided it with a 45-page list of alleged instances of voter fraud. The public radio network did not publish the document, and a White House spokesperson did not respond on Tuesday to a request for a copy.

But in the post-election weeks when Green Party candidate Jill Stein waged battles to recount votes in three swing-states, Trump's lawyers argued in a legal brief that the results should stand because '[a]ll available evidence suggests that the 2016 general election was not tainted by fraud or mistake.'

Catherine Engelbrecht, president of True the Vote, a conservative election watchdog group, told DailyMail.com on Wednesday that she is ' incredibly optimistic that we may be able to finally tackle the very real problems plaguing our election processes.'

'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.'

And the Public Interest Legal Foundation, another right-leaning group, blasted former president Barack Obama for not acting as Trump now pledges he will.

'President Trump’s decision to renew the federal government’s interest in enforcing laws against election fraud and the procedures that work to prevent such activities is important,' the group's president and general counsel J. Christian Adams said in a statement.

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

Spicer faced round after round of hostile questions from journalists who smelled blood in the water after Trump revived his claims of voter fraud on a massive scale

Trump warned repeatedly in October, including at this Cleveland, Ohio rally, that he faced 'a rigged election' because of illegally registered voters and dead people on voter rolls

Brian Fallon, a Clinton campaign official who likely stood to become her White House press secretary, vented Tuesday afternoon on Twitter in the opposite direction.

'Here we go again,' Fallon wrote in a pair of tweets. '@PressSec backs up Trump on patently false statement – this time that voter fraud prevented him from winning [the] popular vote.'

'This is why WH [White House] reporters should never boycott Spicer's briefings. Public needs to see this WH's bogus claims subjected to daily scrutiny.'

Some Republicans are openly skeptical of Trump's views about widespread voter fraud.

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. True The Vote president Catherine Engelbrecht

Arizona Sen. John McCain said Wednesday on 'Morning Joe' that 'there's no evidence of that, and I think that those who allege that have to come up with some substantiation of the claim.'

McCain chuckled that 'I won by 14 points. I'm absolutely sure that there was not a single illegal vote in Arizona.'

On the same MSNBC show, Maryland Democratic Rep. Elijah Cummings fretted that 'this argument about voter fraud ... gives the Republicans and others another tool and another reason to justify to the public of denying people the right to vote.'

Spicer reinforced on Monday that Trump's notion of millions of illegally cast votes is 'a longstanding belief that he's maintained.'

But NPR correspondent Mara Liasson challenged him about why the president wouldn't want to get to the bottom of it.

'If 3 to 5 million people voted illegally, that is a scandal of astronomical proportions,' Liasson declared in the White House press briefing room.

'Doesn't he want to restore Americans' faith in their ballot system? Wouldn't he want an investigation of this? This is a huge, huge scandal.'

'We'll see where we go from here,' Spicer replied. 'But right now the focus that the president has is on putting Americans back to work.'

Spicer, who was the Republican National Committee's chief communicator before moving to the West Wing, declined on Tuesday to say if he personally agrees with Trump's view.

The president made allegations of 'voter fraud' in November, after he won the election, tweeting that he lost the popular vote because of 'millions of people who voted illegally'

House Speaker Paul Ryan told reporters Tuesday at the U.S. Capitol that he has 'seen no evidence to that effect,' referring to Trump's claims. 'I've made that very, very clear.'

The president often warned in the final month of the presidential campaign that voter fraud could cost him the election.

During a late October rally in Cleveland, Ohio, he called it 'a rigged election.'

Citing statistics from the Pew Research Center, Trump said that 'there are 24 million voter registrations in the United States that are either invalid or significantly inaccurate. A lot, right? 24 million. A lot.'

'There are 1.8 million dead people that are registered right now to vote,' he continued.

'And folks, folks: Some of them vote! I wonder why. I wonder how that happens. They woke up from the dead, and they went and voted!'

'There are 2.8 million people who are registered in more than one state,' he mused. So, "We'll vote here, let's ride down the road, let's vote next to it".'

And then, reacting to a fan in the audience, he stopped cold.

'Maybe they'll vote for Trump. I don't know. Maybe I shouldn't be saying this. I may be hurting myself!'

'You're right! You're right,' he responded to the unsolicited advice. 'Maybe they're gonna vote for Trump!'

'Alright,' he laughed, 'let's forget that. It's okay for them to do it!'

Brian Fallon, who would likely have had Spicer's job if she had won the White House, tweeted Tuesday that Trump's view is 'patently false' and slammed Spicer for repeating 'bogus claims'

In a late November conference call with reporters, Trump's senior policy adviser Stephen Miller declined to speculate about a Justice Department investigation, but called voter fraud allegations 'an issue of concern.'

'There's a concern that so many voted who were not legally supposed to,' he said.

On Tuesday, Spicer defended his boss by citing the same Pew study then-candidate Trump crowed about three months ago, but confused its statistics with another piece of research.

'There was one that came out of Pew in 2008 that showed 14 per cent of people who've voted were non-citizens,' he claimed.

That number came from a 2014 Washington Post article by a pair of Old Dominion University professors. It was later challenged by other researchers, who claimed the professors' findings stemmed from 'measurement error.'