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 last fall in the run-up to the election.

While citing no evidence to support his explosive allegation, Trump said in a series of four tweets sent Saturday morning that Obama was “wire tapping” his New York offices before the election in a move he compared to McCarthyism. “Bad (or sick) guy!” he said of his predecessor, adding that the surveillance resulted in “nothing found.”

Trump offered no citations nor did he point to any credible news report to back up his accusation, but he may have been referring to commentary on Breitbart and conservative talk radio suggesting that Obama and his administration used “police state” tactics last fall to monitor the Trump team. The Breitbart story, published Friday, has been circulating among Trump’s senior staff, according to a White House official who described it as a useful catalogue of the Obama administration’s activities.

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

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

Trump has been feuding with the intelligence community since before he took office, convinced that career officers as well as holdovers from the Obama administration have been trying to sabotage his presidency. He has ordered internal inquiries to find who leaked sensitive information regarding communications during the campaign between Russian officials and his campaign associates and allies, including Attorney General Jeff Sessions and ousted national security adviser Michael Flynn.

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

“It’s highly unlikely there was a wiretap,” said one former senior intelligence official familiar with surveillance law who spoke candidly on the condition of anonymity. The former official continued: “It seems unthinkable. If that were the case by some chance, that means that a federal judge would have found that there was either probable cause that he had committed a crime or was an agent of a foreign power.”

A wiretap cannot be directed at a U.S. facility, the official said, without finding probable cause that the phone lines or Internet addresses were being used by agents of a foreign power — or by someone spying for or acting on behalf of a foreign government. “You can’t just go around and tap buildings,” the official said.

Rep. Adam Schiff (Calif.), the ranking Democrat on the House Permanent Select Committee on Intelligence, issued a statement chastising Trump for leveling a “spectacularly reckless allegation” against Obama without evidence.

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

Trump sent the tweets from Palm Beach, Fla., where he is vacationing this weekend at his private Mar-a-Lago estate. It has long been his practice to stir up new controversies to deflect attention from a damaging news cycle, such as the one in recent days about Sessions and Russia.

Trump’s tweets took numerous top White House aides by surprise, according to a second White House official who was not authorized to speak publicly. Saturday was expected to be a “down day, pretty quiet,” this official said, and there was little, if any, attempt to coordinate the president’s message on the wiretapping allegations.

Here are Trump’s tweets, in the order they were sent:

“Terrible! Just found out that Obama had my “wires tapped” in Trump Tower just before the victory. Nothing found. This is McCarthyism!”

“Just out: The same Russian Ambassador that met Jeff Sessions visited the Obama White House 22 times, and 4 times last year alone.”

“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!”

“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!”

“How low has President Obama gone to tapp my phones during the very sacred election process. This is Nixon/Watergate. Bad (or sick) guy!”

Trump did not stop tweeting there. About an hour later, the president revived one of his favorite feuds, this one with Arnold Schwarzenegger. The movie star-turned-California governor has been hosting “The New Celebrity Apprentice,” the NBC reality franchise that Trump helped found.

Schwarzenegger announced Friday that he would not return to the show for another season because, he said, the show had too much “baggage.” But Trump insisted on Twitter that there is more to the story than that.

“Arnold Schwarzenegger isn’t voluntarily leaving the Apprentice, he was fired by his bad (pathetic) ratings, not by me. Sad end to great show”