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President Donald Trump's newest pivot might be his way to divert attention from his own Russia troubles by leveling a Watergate-level conspiracy allegation at former President Barack Obama.

But this latest assertion that Obama ordered illegal surveillance of Trump Tower during the 2016 election tweeted without evidence could get the president into some legal hot water.

Although the law provides a great deal of leeway for political speech, that protection is not all encompassing. And because of the way Trump has leveled unsubstantiated accusations at Obama, he may have libeled his predecessor.

"He's basically stating that Mr. Obama committed crimes, and to state that somebody has committed a crime when it's false is clearly defamatory," said Benjamin Zipursky, who teaches defamation law at Fordham University Law School in New York.

"The question is: Is there enough evidence of serious reckless disregard to send that case to a jury?" Zipursky added. "I don't know what a court would decide on that, but there is some evidence of recklessness."

It's difficult for public figures to win libel cases. Most courts rule against them because the assumption is that they have chosen to make their lives an open book, which means people will talk about them. But past Supreme Court cases have created a basic standard that seeks to answer two legal questions:

The answer to both questions must be yes, and that could be a difficult conclusion to draw.

"What the plaintiff has to show is that the defendant has said, written or tweeted something that is a false statement of fact that harms the reputation of the defendant, and because Obama is a public official, you have to show that it was done with some sort of intent to harm," said Jay Wexler, a professor of constitutional law at Boston University Law School.

Related: What Does It Take to Get a Legal Wiretap?

Despite that high threshold, a fair amount of evidence is beginning to build that Trump might have crossed the legal line.

A senior U.S. official told NBC News that FBI Director James Comey asked the Justice Department over the weekend to publicly reject Trump's claims because they were untrue.

A spokesman for Obama said Sunday that Trump's tweets were "unequivocally false," and James Clapper, the former director of national intelligence, flatly denied any wiretap of Trump Tower on NBC's "Meet the Press."

In addition, it seems that Trump did not try to ask his own administration whether the scenario was true. A senior U.S. official in a position to know told NBC News that Trump "did not consult with the people inside the U.S. government who might know before making this claim."

Then, on Sunday, the White House called for a congressional investigation into illegal wiretapping of the Trump campaign.

"President Donald J. Trump is requesting that as part of their investigation into Russian activity, the congressional intelligence committees exercise their oversight authority to determine whether executive branch investigative powers were abused in 2016," White House Press Secretary Sean Spicer said.

As the evidence that Trump's charge is false piles on top of the proof that he did not try to fact-check it, experts say he is treading on troubling ground.

"I think the plaintiff would claim that it's untrue and the burden would be on Trump, the defendant, to prove truth," Wexler said.

Trump himself has threatened lawsuits against many people and publications since he entered the public eye, but he brought only seven of those cases to court, according to USA Today. Of those seven, he won only one.

Despite the possible case, it is unlikely that Obama would sue Trump for libel. Predecessors tend to give the succeeding president a fair amount of room, and the president is provided some protections from civil suits. The Supreme Court's 1982 decision Nixon v. Fitzgerald found that a president is provided absolute immunity from civil damages and liability while conducting presidential acts.

"President Trump has official immunity from liability and damages," Zipursky confirmed, but it is not clear that judges would view tweeting a defamatory conspiracy theory, without evidence, as a president carrying out his official duties.

Read more:
Analysis: Does Obama Have Grounds to Sue Trump for Libel? - NBCNews.com