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A day after President Donald Trump claimed without evidence that the Obama administration had wiretapped him when he was a candidate, the White House sought to spin it as merely a request for more information and called on Congress to investigate.

"All we're saying is let's take a closer look. Let's look into this. If this happened, if this is accurate, this is the biggest overreach and the biggest scandal," White House spokeswoman Sarah Huckabee Sanders said on ABC News.

That's not all the president said, however, when he spoke of the allegations as fact.

"This is Nixon/Watergate," he wrote. NBC News has not found any evidence to substantiate Trump's wiretapping claims.

White House Press Secretary Sean Spicer released a statement that offered no evidence, instead saying the White House wouldn't comment until Congress had investigated his claims.

The president "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," the statement said.

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The White House's careful attempt to shift Trump's unequivocal allegations into a call for investigation comes just 24 hours after the president's tweet storm early Saturday morning, when he said he'd learned he'd been wiretapped. He offered no evidence, and, in the last day, both Republicans and Democrats have called on the White House to provide evidence to substantiate the claims.

Related: Former DNI James Clapper: 'I Can Deny' Wiretap of Trump Tower

Sanders said the president was "going off of information that he's seen that has led him to believe that this is a very real potential." But she also said that she hadn't heard the president's allegations before he tweeted them and that she couldn't "speak 100 percent" as to whether Trump consulted others before tweeting them out.

"I'm not sure," she said.

A spokesman for Obama disputed Trump's claims, saying any accusation that the White House or Obama's administration ordered such surveillance is "simply false."

On "Meet the Press," the Obama administration's director of national intelligence, James Clapper, said that, under his watch, "there was no wiretap activity mounted against the president-elect at the time or as a candidate or against his campaign."

A senior U.S. official confirmed to NBC News on Sunday that FBI Director James Comey — a holdover from the Obama administration — asked Justice Department officials to publicly reject Trump's claims. The request was first reported by The New York Times.

To be legal, any such surveillance would have to be authorized by the Foreign Intelligence Surveillance Court, called the FISA court, which operates in secrecy.

Democrats on the House Judiciary Committee demanded Sunday that White House counsel Donald McGahn respond to a Times report that his office had sought to gain access to an order he believed may have been issued by the FISA court. Such an effort would be "inappropriate" and "improper," the lawmakers said in a letter to McGahn obtained by NBC News.

"The independence of the Department of Justice and the FBI is a particular concern when individuals associated with both the Administration and the President's campaign may be the targets of the investigation," the lawmakers said.

Meanwhile, the committees the White House has called on to investigate toed a fine line. Democrats sought to politicize the president's unsubstantiated claims, and Republicans worked to stay out of the fray.

Richard Burr of North Carolina, the Republican chairman of the Senate Select Committee on Intelligence, said his committee "will follow the evidence where it leads."

Related: Analysis: The Quiet Response to President Trump's Explosive Claim

The Republican chairman of the House Select Committee on Intelligence Chairman, Devin Nunes of California, released a statement saying the committee would "investigate this issue if the evidence warrants it," while noting that this wasn't a change — the committee's investigation already involved the U.S. government's actions.

The ranking Democrat on the same committee, Adam Schiff of California, slammed the president.

"Today, it became all the more clear that President Trump's claim that he was illegally wire-tapped by President Obama was based on little more than Breitbart or other conspiracy-based news," he said in part. "Sean Spicer today tweeted that the Administration would have no further comment until this matter was investigated and who can blame him: not even Spicer wishes to have to speak to such a unsubstantiated charge."