President Trump on Saturday angrily accused former president Barack Obama of orchestrating a “Nixon/Watergate” plot to tap the phones at his Trump Tower headquarters in the run-up to last fall’s election, providing no evidence to support his explosive claim and drawing a flat denial from Obama’s office.

Leveling the extraordinary allegation about his predecessor in a series of four early morning tweets, Trump said Obama had been “wire tapping” his New York offices and suggested that the former president had meddled with the “very sacred election process.” Obama’s supposed actions, Trump said, amounted to McCarthyism.

“Bad (or sick) guy!” the 45th president tweeted about the 44th, insisting that the surveillance efforts resulted in “nothing found.”

Senior U.S. officials with knowledge of a wide-ranging federal investigation into Russian interference in the election, who spoke on the condition of anonymity to discuss classified information, said Saturday that there had been no wiretap of Trump.

Kevin Lewis, a spokesman for Obama, said in a statement: “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. 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.”

President Trump speaks to Navy and shipyard personnel aboard nuclear aircraft carrier U.S.S. Gerald R. Ford in Newport News, Va., on Thursday, March 2. (Jabin Botsford/The Washington Post)

Officials at the FBI and the Justice Department declined to comment.

According to senior administration officials, White House Counsel Donald McGahn and his office are inquiring about possible surveillance of then-candidate Trump while being sensitive to legal and national security considerations.

White House press secretary Sean Spicer said McGahn “is reviewing what options, if any, are available to us.”

It could not be immediately determined whether there had been wiretaps of anyone in Trump’s orbit who might be a subject of the Russia probe. Sen. Christopher A. Coons (D-Del.) told MSNBC on Friday that he believes “transcripts” exist that would show whether Russian officials colluded with Trump’s campaign.

Wiretaps in a foreign intelligence probe cannot legally be directed at a U.S. facility without probable cause — reviewed by a federal judge — that the phone lines or Internet addresses at the facility were being used by agents of a foreign power or by someone spying for or acting on behalf of a foreign government.

Ben Rhodes, a longtime national security adviser to Obama, tweeted at Trump: “No President can order a wiretap. Those restrictions were put in place to protect citizens from people like you.”

Neither Trump nor his aides offered any citation to back up Trump’s accusation about Obama. Trump may have been prompted by a report on the conservative website Breitbart and commentary from talk radio host Mark Levin suggesting that the Obama administration used “police state” tactics to monitor the Trump team. The Breitbart report circulated among Trump’s senior aides Friday and early Saturday, and Trump may have simply been reacting to the piece when he took to his preferred megaphone, Twitter, to trumpet his claim.

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Trump’s tweets punctuated a general feeling shared by the president, his advisers and allies that Obama and the “Deep State” of critics within the intelligence community — who they think are fueling stories on Trump and Russia — have been conspiring to derail his presidency. At the heart of each of the president’s tweets is Trump’s apparent belief that Obama himself — as opposed to members of his administration — had been personally overseeing surveillance of Trump Tower.

The conservative media landscape — including Sean Hannity’s show on Fox News and Infowars, the conspiracy website run by Alex Jones, outlets on which Trump has appeared — has in recent days given birth to tales of Obama and his closest confidants trying to spur Trump’s impeachment or force his resignation.

But separately, the president is furious that a slow churn of revelations about communications between Attorney General Jeff Sessions, ousted national security adviser Michael Flynn and other Trump associates and Russian officials has overshadowed the early weeks of his administration. And he has grown fixated on identifying leakers.

“He’s angry, and he thinks that the leaks — even forgetting the rhetoric on politics — are a significant problem that hurts the security of the country,” said Thomas J. Barrack Jr., a close friend who chaired Trump’s inauguration. “He feels if he can’t rely on his team, if he were negotiating with North Korea on something sensitive and death by a thousand leaks continued, he views that as really being disruptive to the security of America.”

Trump has directed his aides to investigate employees across the federal government, with a particular focus on holdovers from the Obama administration and career intelligence officers, who Trump believes are trying to sabotage him.

White House chief strategist Stephen K. Bannon has been in close touch with the president about what he has called the Deep State. Bannon’s remarks in a recent speech about the “deconstruction of the administrative state” were designed in part to raise alarm among activists on the right about entrenched bureaucrats in the intelligence and defense agencies, according to White House officials.

Roger Stone, a longtime political adviser to Trump who does not work in the administration but still talks with the president, said he is urging Trump to fire and prosecute anyone who leaks damaging information.

“What the president doesn’t understand is he has more power than he knows,” Stone said. “He needs to clean house. Just clean house! Hand the pink slips to everybody. . . . Lock them out of their offices and tell the FBI to start going through their emails and phone messages.”

Trump was incensed over Sessions’s decision to recuse himself from the Russia probe after The Washington Post reported that Sessions had met twice with the Russian ambassador but then testified falsely at his Senate confirmation hearing that he “did not have communications with the Russians.”

In the Oval Office on Friday morning, Trump fumed at his senior staff about the Sessions situation and told them that he disagreed with the attorney general’s move, according to senior White House officials who were not authorized to speak publicly.

Trump told aides that he thought the White House and Justice Department should have done more to counter the argument that Sessions needed to step away. Trump said he wanted to see his staff fight back against what he saw as a widespread effort to destabilize his presidency, the officials said.

Trump then departed for Palm Beach, Fla. — in what one associate described as “a [expletive] bad mood” — to spend the weekend at his private Mar-a-Lago Club, where he fired off Saturday morning’s tweets alleging wiretaps.

Trump amended his public schedule Saturday to add an early evening meeting with Sessions and Homeland Security Secretary John F. Kelly, as well as dinner with both men and other advisers, including Bannon.

If the Foreign Intelligence Surveillance Court approved a wiretapping order on one of Trump’s associates, that would mean the federal judge involved had decided there was probable cause that the person was colluding with a foreign government.

Some current and former intelligence officials cast doubt on Trump’s wiretapping assertion.

“It’s extremely unlikely that there would have been any sort of criminal or intelligence surveillance of Trump,” said Jennifer Daskal, a former senior Justice Department national security official. “There’s no credible evidence yet to suggest that that happened. It would be an extraordinary measure for the FBI to ask for and the court to grant a surveillance order on a presidential candidate of the opposing party in an election year.”

Most Republican leaders were quiet on the issue Saturday, but Sen. Lindsey O. Graham (R-S.C.) vowed at a town hall meeting with constituents to “get to the bottom of this.” He said it would be “the biggest scandal since Watergate” if Obama illegally spied on Trump or if a judge approved a warrant to monitor Trump’s campaign for possible communications with Russia.

“I’m very worried that our president is suggesting that the former president has done something illegally,” Graham said. At the same time, because of what it would signal, “I would be very worried if in fact the Obama administration was able to obtain a warrant lawfully about Trump campaign activity with foreign governments.”

Sen. Ben Sasse (R-Neb.) called for Trump to provide the public more information about his charges. “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.

Democrats, meanwhile, blasted Trump. Rep. Adam B. Schiff (Calif.), the ranking Democrat on the House Permanent Select Committee on Intelligence, said the president leveled a “spectacularly reckless allegation” against Obama without evidence.

Referencing Trump’s description of Obama as a “bad (or sick) guy,” Schiff said in a statement, “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.”

Daskal, who now teaches law at American University, agreed. “It is extremely dangerous for the president to be suggesting that he was being surveilled for political purposes, when there is absolutely no evidence of that fact,” she said.

Jenna Portnoy in Palm Beach, Fla., and David Weigel and Matt Zapotosky in Washington contributed to this report.