Legal analysis

On Monday, the FBI raided the law office of Michael Cohen, President Donald Trump's personal lawyer. They were seeking information about a $130,000 payment Cohen says he personally made to adult film star Stormy Daniels days before the 2016 election, sources told NBC News.

The search warrants were sought and executed by FBI agents and federal prosecutors in New York in coordination with special counsel Robert Mueller's team after an initial referral from Mueller's office.

The Fourth Amendment provides that "no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized." A valid search warrant rests on a finding that there is probable cause to believe that (1) a crime has been committed and (2) evidence of the crime will be found in the place to be searched. "Probable cause" means the FBI would have to demonstrate to a magistrate that there was a substantial chance evidence of criminal activity would be found in Cohen's offices, or in a hotel where he was living, which was also searched.

Federal prosecutors may have executed this search warrant for the premises of an attorney because Cohen may be a subject of an investigation. But, as an attorney, he is also engaged in the practice of law on behalf of clients — clients whose privileged materials are now in the possession of federal agents. Among those clients is the sitting president of the United States.

According to Department of Justice policy, an application for a search warrant of a lawyer's office such as this is so serious that it usually requires approval of either the U.S. attorney for the district, or the assistant attorney general.

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Because of the potential damage to legitimate attorney-client relationships caused by these mass seizures of records, U.S. attorneys are trained to explore alternatives to these warrants when evidence is sought from a practicing attorney. One alternative would be a subpoena, which allows the attorney to search for and produce the documents. The fact that the FBI opted for a raid without notice suggests prosecutors believed less-intrusive measures might result in the destruction of evidence.

Now that the documents are in the FBI's possession, the U.S. attorney's manual mandates the use of procedures that ensure privileged materials are not improperly viewed, seized or retained. We know that as an attorney, Cohen had at least one active client: Trump called Cohen his lawyer on Air Force One just days ago.

Trump on Tuesday morning tweeted: "Attorney-client privilege is dead!"

The privilege is not dead. It's just that that the privilege alone won't prevent the issuance of a search warrant for documents in an attorney's office.

Of course, the privilege between an attorney like Cohen and his clients may be lost if the "crime-fraud exception" applies. The purpose of this exception is to assure that the secrecy between lawyer and client does not extend to obtaining advice in furtherance of contemplated or ongoing criminal or fraudulent conduct.

It is not enough for the government to just show that these privileged communications between Cohen and a client might provide evidence of a crime. Rather, the communication itself must have been in furtherance of, and intended to facilitate the crime, in order to strip these communications of the protections of privilege.

Cohen's office potentially contains documents and communications to all his clients — not just Trump — that are privileged and confidential. The documents must be reviewed for privilege claims, and privileged documents are supposed to be returned to the attorney from whom they were seized.

Of course, this raises a thorny issue: How do the agents and prosecutors review the documents for privilege status, if the entire point of privilege is that it's not supposed to be seen by people outside the lawyer's office, particularly members of law enforcement?

The U.S. attorney's manual proposes a solution to that conundrum: A "taint team." Also called a "privilege team," this is a group, consisting of agents and lawyers not involved in the underlying investigation, brought in to review the privileged documents.

If this sounds like a strange fix, some courts agree, and have expressly disapproved of the government's use of taint teams to review documents, including the federal court in the same district where the search of Cohen's office occurred.

Some courts have even held that where the government uses a taint team, the government bears the burden to rebut the presumption that tainted material was improperly provided to the prosecution. Other courts have suggested that it would be preferable for the privilege review to be done by magistrate judge, and not a privilege team comprised of DOJ agents and lawyers.

Danny Cevallos is an MSNBC legal analyst. Follow @CevallosLaw on Twitter.