WEST PALM BEACH, Fla. — President Trump on Saturday accused former President Barack Obama of tapping his phones at Trump Tower the month before the election, taking to Twitter to call his predecessor a "bad [or sick] guy."
Without offering any evidence or providing the source of his information, Trump fired off a series of Twitter messages contending that Obama "had my 'wires tapped." He likened the supposed tapping to "Nixon/Watergate" and "McCarthyism."
A spokesman for the former president said any suggestion that Obama had ordered such surveillance was "simply false."
Trump's aides declined to clarify whether the president's explosive allegations were based on briefings from intelligence or law enforcement officials — which could mean that Trump was revealing previously unknown details about an investigation — or on something else, like a news report.
His decision to lend the power of his office to such a charged claim against his predecessor — without offering any initial proof — was remarkable, even for a leader who has repeatedly shown himself willing to make assertions that are false or based on dubious sources.
It would have been difficult for federal agents, working within the law, to obtain a wiretap order to target Trump's phone conversations.
It would have meant that the Justice Department had gathered sufficient evidence to persuade a federal judge that there was probable cause to believe he had committed a serious crime or was an agent of a foreign power, depending on whether it was a criminal investigation or a foreign intelligence one.
Former officials pointed to longstanding laws and procedures intended to ensure that presidents cannot wiretap a rival for political purposes.
"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," said Kevin Lewis, a spokesman for Obama. "As part of that practice, neither President Obama nor any White House official ever ordered surveillance on any US citizen."
But a senior White House official said Donald F. McGahn II, Trump's chief counsel, was seeking access Saturday to what the official described as a document issued by the Foreign Intelligence Surveillance Court authorizing surveillance of Trump and his associates.
The official offered no evidence to support the notion that such a document exists; any such move by a White House counsel would be viewed at the Justice Department as a stunning case of interference.
It has been widely reported that there is a federal investigation, which began during the 2016 presidential campaign, into links between Trump associates and the Russians. That issue has dogged Trump for months.
In one message, which Trump sent from his Palm Beach, Fla., estate at 6:35 a.m., the president said he had "just found out" that his phones had been tapped before the election. Trump's reference to "wires tapped" raised the possibility that he was referring to some other type of electronic surveillance and was using the idea of phone tapping loosely.
Two people close to Trump said they believed he was referring to a Breitbart News article, which aides said had been passed around among his advisers. Mark Levin, a conservative radio host, had also embraced the theory recently in a push against what right-leaning commentators have been calling the "deep state."
The Breitbart article, published Friday, contended that there was a series of "known steps taken by President Barack Obama's administration in its last months to undermine Donald Trump's presidential campaign and, later, his new administration."
If Trump was motivated to take to Twitter after reading the Breitbart article or listening to Levin, he was using a presidential megaphone to spread dark theories of a broad conspiracy aimed at undermining his presidential ambitions, and later his presidency.
Even with the Breitbart article circulating, several of Trump's advisers were stunned by the president's morning Twitter outburst. Those advisers said they were uncertain about what specifically Trump was referring to; one surmised that he may also have been referring to a months-old news report about a secret surveillance warrant for communications at his New York offices.
One senior law enforcement official from the Obama administration, who has knowledge of the FBI investigation into Russia and of government wiretapping, said it was "100 percent untrue" that the government had wiretapped Trump.
The official, who asked for anonymity to discuss matters related to investigations and intelligence, said the White House owed the American people an explanation for the president's allegations.
Ben Rhodes, a former top national security aide to Obama, said in a Twitter message directed at Trump on Saturday that "no president can order a wiretap," and added, "Those restrictions were put in place to protect citizens from people like you."
The House and Senate Intelligence Committees are moving forward with their own investigations into Russia's efforts to influence the election, and they have said they will examine links between Trump's associates and the Russians.
Senator Chris Coons, Democrat of Delaware, said on Friday that he believed there were "transcripts" that would help document those contacts, though he said he had not yet seen them.
"There are transcripts that provide very helpful, very critical insights into whether or not Russian intelligence or senior Russian political leaders — including Vladimir Putin — were cooperating, were colluding, with the Trump campaign at the highest levels to influence the outcome of our election," Coons told Andrea Mitchell on MSNBC. "I believe they exist."
The New York Times reported in January that among the associates whose links to Russia are being scrutinized are Paul Manafort, Trump's onetime campaign chairman; Carter Page, a businessman and foreign policy adviser to the campaign; and Roger Stone, a Republican operative who said he was in touch with WikiLeaks at one point before it released a trove of e-mails from John D. Podesta, Hillary Clinton's campaign chairman, last August.
Stone later said he had communicated with WikiLeaks through an intermediary.
Trump appeared on Saturday to suggest that warrants had been issued by the Foreign Intelligence Surveillance Court. He contended that the Obama administration had once been "turned down by court" in its supposed efforts to listen in on conversations by Trump and his associates.
In the fall, the FBI examined computer data showing an odd stream of activity between a Trump Organization server and Alfa Bank, one of Russia's biggest banks, whose owners have long-standing ties to Putin.
While some FBI officials initially believed that the computer activity indicated an encrypted channel between Moscow and New York, the bureau ultimately moved away from that view. The activity remains unexplained.
There is no confirmed evidence that the FBI obtained a court warrant to wiretap the Trump Organization or was capturing communications directly from the Trump Organization.
During the transition, the FBI — which uses FISA warrants to eavesdrop on the communications of foreign leaders inside the United States — overheard conversations between the Russian ambassador to the United States and Michael T. Flynn, whom Trump had named national security adviser.
Trump has pointedly and repeatedly questioned in conversations how it was that Flynn's conversations were recorded, and wondered who could have issued a warrant.
After The Washington Post reported that Flynn and the ambassador, Sergey I. Kislyak, had discussed sanctions that the Obama administration had just imposed on Russia, Flynn was pushed out of his post by the White House because he had lied to Vice President Mike Pence about the calls.
The Breitbart article cited mainstream news reports and concluded — going beyond the public record — that the Obama administration had "obtained authorization to eavesdrop on the Trump campaign; continued monitoring the Trump team even when no evidence of wrongdoing was found; then relaxed the NSA rules to allow evidence to be shared widely within the government."
Levin, a day earlier, railed about what he called a "much bigger scandal," contending — again with no evidence — that Obama and his aides had used "the instrumentalities of the federal government, intelligence activity, to surveil members of the Trump campaign and put that information out in the public."
Several senior members of Trump's White House staff, including his spokesman, Sean Spicer, did not respond to an e-mail requesting on-the-record responses to more than a half-dozen questions about Trump's Twitter posts.
Terrible! Just found out that Obama had my "wires tapped" in Trump Tower just before the victory. Nothing found. This is McCarthyism!— Donald J. Trump (@realDonaldTrump) March 4, 2017
Is it legal for a sitting President to be "wire tapping" a race for president prior to an election? Turned down by court earlier. A NEW LOW!— Donald J. Trump (@realDonaldTrump) March 4, 2017
I'd bet a good lawyer could make a great case out of the fact that President Obama was tapping my phones in October, just prior to Election!— Donald J. Trump (@realDonaldTrump) March 4, 2017