President Donald Trump alleged in a tweet storm early Saturday that former President Barack Obama had wiretapped Trump Tower before his election win in November — an accusation that a senior U.S. official told NBC News is baseless.
Trump did not provide any evidence for the claims, which followed an interview on Fox News in which the allegation came up.
In response, Obama spokesman Kevin Lewis roundly rejected Trump's claims that the previous administration had ordered surveillance at his New York City residence.
"A cardinal rule of the Obama administration was that no White House official ever interfered with any independent investigation led by the Department of Justice," Lewis said. "As part of that practice, neither President Obama nor any White House official ever ordered surveillance on any U.S. citizen. Any suggestion otherwise is simply false."
A senior U.S. official in a position to know told NBC News that Trump's allegations have no merit, and the president did not consult with people within the U.S. government who would know the validity of the charge before making claims on his favored communications platform.
"Terrible! Just found out that Obama had my 'wires tapped' in Trump Tower just before the victory. Nothing found. This is McCarthyism!" Trump wrote as part of a series of tweets Saturday morning.
An FBI spokeswoman said the bureau would not comment on the tweets.
NBC News reached out to the White House for comment, but did not immediately hear back.
Ben Rhodes, former deputy national security adviser to Obama, said in a tweet that presidents can't simply order wiretaps as Trump suggests.
Rep. Adam Schiff, D-Calif., the ranking member of the House Permanent Select Committee on Intelligence, said Trump's tweets displaying a worrying trend.
"If there is something bad or sick going on, it is the willingness of the nation's chief executive to make the most outlandish and destructive claims without providing a scintilla of evidence to support them," Schiff said in a statement.
On Friday, Fox's Brett Baier asked House Speaker Paul Ryan whether he was concerned "that the Obama administration may have been surveilling members of the Trump campaign in a pretty detailed investigation during the election?"
Ryan responded by saying: "I don't think that's the case."
Trump, who is spending the weekend at his Mar-a-Lago resort in Florida, frequently tweets about topics that have appeared in conservative media outlets.
NBC News has found no evidence to support Trump's claims about wiretapping, which appear to stem from conservative media outlets, such as Breitbart, and anonymously sourced reports in British blogs. According to those reports, U.S. officials obtained a warrant under the Foreign Intelligence Surveillance Act (FISA) to investigate contacts between computers at a Russian bank and a server inside Trump's campaign headquarters at Trump Tower.
A FISA warrant would allow the FBI to intercept communications outside of the normal criminal process, but they would likely require the permission of a magistrate judge to extensively wiretap Trump Tower.
There have been reports that communications between Trump associates and Russians were picked up by intelligence agencies during the campaign as part of routine surveillance of the Russians. Trump and his aides have denied there were any improper contacts.
After a rowdy town hall in Clemson, South Carolina, on Saturday, Republican Sen. Lindsey Graham said that if true, the allegations would be the "biggest political scandal since Watergate" and vowed to get to the bottom of Trump's claims.
He later told NBC News that there are three possibilities for what occurred: "It's all a misunderstanding, the Obama administration went way out of line or some judge somewhere said there's something to the idea of the Trump Russia ties," Graham said.
Republican Sen. Ben Sasse called on Trump to provide evidence for the explosive wiretapping claim. He said that if the alleged wiretap Trump was referring to was without authorization of the FISA court, "the President should explain what sort of wiretap it was and how he knows this."
"We are in the midst of a civilization-warping crisis of public trust, and the President's allegations today demand the thorough and dispassionate attention of serious patriots," Sasse said in a statement. "A quest for the full truth, rather than knee-jerk partisanship, must be our guide if we are going to rebuild civic trust and health."
Trump's allegations about Obama were part of a flurry of early-morning tweets that also defended Attorney General Jeff Sessions.
Sessions is under fire for not disclosing during his confirmation hearing that he met with Russian Ambassador Sergey Kislyak. Sessions was a senator at the time and an adviser to the Trump campaign.
"The first meeting Jeff Sessions had with the Russian Amb was set up by the Obama Administration under education program for 100 Ambs......"
"The same Russian Ambassador that met Jeff Sessions visited the Obama White House 22 times, and 4 times last year alone," Trump tweeted.
News of the meetings drew fire from critics who said Sessions had misled the Judiciary Committee in his January confirmation hearings.
Sessions recused himself from overseeing any Justice Department investigation into alleged Russian election interference earlier this week.
On Friday, he said he would submit amended testimony and respond to senators' questions over his contacts with Russia's ambassador.
Sessions faces calls for his resignation over the issue but Trump has backed his attorney general, saying he did nothing wrong.
In recent days, Trump has swiped back at allegations about the communications between members of his team and Russian officials during and after the campaign.
He lashed out at Democrats Chuck Schumer and Nancy Pelosi Friday, tweeting a picture of Schumer meeting Russian President Vladimir Putin in 2003.
He also retweeted a Politico article which revealed Pelosi had met the Russian ambassador in 2010 despite her claims to the contrary.
Trump said both Democrats should also be investigated for their ties to Russia.
Schumer responded on the social network: "Happily talk re: my contact w Mr. Putin & his associates, took place in '03 in full view of press & public under oath. Would you & your team?"
On Feb. 13, National Security Adviser Michael Flynn resigned shortly after The Washington Post first reported that the Justice Department had informed the White House that Flynn might be subject to blackmail by Moscow.
Trump acknowledged in January that Russia had a role in a series of cyberattacks on America, but says it didn't impact the election.