Early morning Saturday President Donald Trump made several tweets that accused his predecessor of  conducting a “Nixon/Watergate” wiretapping scheme on Trump Tower during the election. Trump is staying the weekend at his private Mar-a-Lago resort in Palm Beach, Florida, and he offered no evidence of his wiretapping claims, which he called “McCarthyism!”

It’s not exactly clear what Trump is referencing—or whether the information was based on intelligence briefings from law enforcement, or just gleaned from media reports. It has been widely reported that there’s an ongoing investigation that began in 2016 into possible links between Trump’s close associates and top Russian officials, including a report issued by American intelligence agencies in January that concluded the Russian government sought to influence the election on Trump’s behalf.  

Obama’s spokesman, Kevin Lewis, issued a short response to Trump’s allegations, saying "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."

There have been reports that the FBI sought approval last summer to monitor members of the Trump team suspected of having irregular talks with the Russians. Ali Soufan, chair of the Soufan Group security firm and a former FBI agent, noted that such requests must be sanctioned by federal judges.

“The president cannot order criminal wiretaps or any other kind of wiretaps,” said Soufan. “No president can."

The process for obtaining a federal wiretap, either for domestic crimes or for foreign intelligence purposes, involves the approval and supervision of a federal judge. Those requests are made by investigators themselves, and the president is ultimately briefed on them only if Justice Department officials believe it is necessary.

“They deliberately withhold that because they don't want the president to get involved in an ongoing investigation," said Clint Watts, a fellow at the Foreign Policy Research Institute and a former FBI special agent. "They play by a really strict rulebook at DoJ."

Bruce Green, a law professor at Fordham and a former federal prosecutor said a president ordering a wiretap would be unusual, to say the least.

“It would obviously be improper for the government to seek wiretap authorization for partisan political purposes, rather than legitimate criminal investigative or national security purposes as set out in the application to the court,” said Green. “In prior administrations, if a President directed the Attorney General or another government lawyer to seek wiretap authorization for illegitimate reasons, the lawyer would have been expected to try to dissuade the President and, if the President persisted in giving this order, to refuse and/or resign.”

A judge would also likely refuse such a request. “An ethical government lawyer would be expected to disclose the President's involvement to the court, which could then be expected to deny authorization,” Green said.

If, hypothetically, a judge did approve a warrant for electronic surveillance of Trump officials, that would mean the judge was persuaded there was probable cause to believe they were going to commit a crime or were communicating with agents of a foreign power––and that the gravity of the circumstances justified approving the request, even in the face of the massive potential political fallout.

Reports have also suggested that former National Security Adviser Mike Flynn’s conversations with the Russian Ambassador Sergey Kislyak were picked up during surveillance of Kislyak. The FBI sometimes eavesdrops on foreign leaders while in the U.S., and it is possible that agents overheard Flynn’s conversation while monitoring Kislyak’s phone line. Flynn ultimately resigned, after it was reported that he misled administration officials about the content of his conversations with Kislyak.

Another possible impetus for the president’s tweets could have come from comments made Thursday by conservative radio host Mark Levin. On his show, Levin said Obama had tried to undermine the Trump campaign by eavesdropping, calling the former president’s administration a “police state.” Levin then demanded a Congressional investigation, and his comments were picked up by Breitbart, the website formerly run by Steve Bannon, Trump’s chief strategist*.

According to The Washington Post, the Breitbart story was being circulated among Trump’s senior staff before the weekend. Trump’s mood before he left to his resort Friday, The New York Times reported, seemed to “be explosive”, and the president reportedly railed about leaks in his staff and among federal intelligence agents.

But Trump’s ire did not end with Obama Saturday morning.

Trump capped off his tweetstorm with a comment on his reality TV show replacement, Arnold Schwarzenegger.

* This article originally stated that Trump White House adviser Stephen Bannon founded Breitbart News; he was formerly its executive chairman. We regret the error.