Updated at 12:11 p.m.

Whatever evidence federal prosecutors have collected concerning Michael Cohen, President Trump’s longtime attorney, it is most likely extraordinarily strong.

Before federal agents raided Cohen’s home, hotel room, and office Monday afternoon, they would have had to convince high-ranking officials at the Department of Justice and a federal judge that a search warrant was necessary to obtain the evidence sought.

“Doing a search warrant rather than a subpoena suggests the investigators thought Cohen, if given a subpoena, would possibly destroy evidence or withhold key evidence, particularly if it were incriminating,” Clinton Watts, a former FBI agent and a senior fellow at the Foreign Policy Research Institute, said.

Under normal circumstances, obtaining a search warrant on an attorney for the subject of a federal investigation is an incredibly aggressive move. When the attorney’s client is the president of the United States, the stakes couldn’t possibly get any higher.

“These things are not anonymized, so you know you’re talking about Michael Cohen, the longtime attorney for the person who is now president of the United States, so you know you’re in very deep water,” John Q. Barrett, a former associate special counsel in the Iran-Contra affair and a law professor at St. Johns, said. “Any law-enforcement official would proceed very carefully.”

The raid, first reported by The New York Times, is an extraordinary development in a story that was already incredibly strange. Cohen wired $130,000 to adult actress Stormy Daniels in late 2016, during the waning days of the presidential campaign, in order to prevent her from speaking out about her alleged affair with Trump. A longtime employee of the Trump Organization and one of the president’s personal attorneys, Cohen has reportedly been under scrutiny by Special Counsel Robert Mueller, who is investigating the Russian effort to sway the 2016 election on Trump’s behalf, and whether the Trump campaign aided that effort. It’s unclear whether the raid is related to the special counsel’s investigation, or a separate inquiry being pursued by the U.S. Attorney’s Office in the Southern District of New York.

The raid was reportedly conducted after Mueller went to Deputy Attorney General Rod Rosenstein with evidence, and Rosenstein referred the matter to the U.S. attorney for the Southern District, Geoffrey Berman (Berman reportedly recused himself). According to the Times, federal agents seized “business records, emails, and documents related to several topics,” including Cohen’s payment to Daniels, and “privileged communications” between Cohen and his clients, according to Cohen’s attorney.

“You don’t just have to have the evidence that the documents may or may not exist, you have to show that there’s no other way to get them besides serving a warrant on the attorney, because of the sensitivity of attorney-client privilege,” David Gomez, a former FBI agent and a fellow at George Washington University’s Center for Cyber and Homeland Security, said.

On Tuesday, Trump tweeted “WITCH HUNT” and “Attorney–client privilege is dead!”

Some of the president’s supporters in the conservative press have been invoking attorney-client privilege, the legal rule that says communications between an attorney and a client are typically protected. But there are important exceptions.

“Records of conversations between Mr. Cohen and Mr. Trump are not necessarily privileged,” Bruce Green, a former federal prosecutor and a law professor at Fordham University, said. “If the conversations do not relate to a legal representation, but Mr. Cohen was providing business assistance or other non-legal services, the privilege probably will not apply.”

There is also something known as the crime-fraud exception to attorney-client privilege. “When the communications between an attorney and client are in furtherance of criminal activity, it’s viewed as an exception to attorney-client privilege,” Barrett said.

In cases where an attorney’s records are seized, a separate team of federal investigators, known as a “taint team,” will go through those records and sort out which are protected, and which prosecutors will be allowed to see or use. “There are various other limitations and exceptions that could make the privilege inapplicable. If it isn’t clear whether documents are privileged, the issue may get litigated,” Green said.

One thing prosecutors are reportedly examining are Cohen’s payments to Daniels. Cohen has said he drew on his home-equity line of credit from First Republic Bank in Manhattan to obtain the funds. Even if the evidence seized from Cohen was sought for a different investigation, if federal prosecutors uncover evidence related to the special counsel’s Russia inquiry, Mueller will have access to it. “Whatever the returns of these searches are, if relevant to Mueller’s work, it will become available to him,” Barrett said.

Trump was furious about the raid, calling the move “an attack on our country, in a true sense,” and “an attack on what we all stand for.” He also said that the prosecutors involved “have the biggest conflicts of interest I have ever seen. Democrats—all. Either Democrats or a couple of Republicans who worked for President Obama.”

Being a Republican, of course, has never stopped Trump from calling for criminal investigations of his Democratic political rivals, no matter how flimsy the pretext. But as my colleague David Graham points out, virtually all the major players involved here are Republicans. Mueller is a Republican who was appointed by George W. Bush to run the FBI. Rosenstein, the deputy attorney general, is an appointee of Trump himself, and so is Chris Wray, the current director of the FBI. Berman, the U.S. attorney whose office executed the raid, is a former law partner to Trump surrogate Rudy Giuliani, who was hand-picked by Attorney General Jeff Sessions. The warrant sought not only would have had to have been approved by officials at the Department of Justice, but a federal judge would have had to sign off on it, knowing that he would be sanctioning a raid against the personal attorney of a sitting president.

Evidently, they all signed off anyway.