For decades, there has been such a thing as the attorney client privilege. In our system of justice, we depend on lawyers who represent clients zealously. To protect that representation, we have developed this attorney client privilege. Until Watergate, the privilege applied to every communication between a lawyer and his/her client. But, the Watergate conspiracy had many facets, one of which was some lawyers refusing to answer questions based on the attorney client privilege. Many of the Watergate actors were lawyers, so the privilege was invoked many times. So, among the many Watergate reforms, the American bar Association re-looked the attorney client privilege.
The ABA researchers modified the privilege. They recommended that it not apply to planned or future crimes. Yes, zealous representation is still critical to our judicial system. But, said, the ABA committee, zealous representation is not as important as preventing crime and harm to others.
So, when Pres. Trump says the attorney client privilege is dead, he is wrong. He exaggerates, of course, but even allowing for hyperbole, he is wrong. The attorney client privilege has not included crimes yet to be committed for several decades. We do not know yet what supported the search warrant for Michael Cohen. But, with all the multiple layers of review it received, it is very likely the U.S. Attorney for the Southern District of New York is looking at possible crimes, yet to be committed. See Politico news report.
And, by the way, it is not unheard of for law enforcement agencies to seize documents from successful criminal defense attorneys. It is rare to do so, but it happens. Some law enforcement agencies become convinced that some defense lawyer, especially after winning a few trials, are committing crimes him or herself. So, sure, they might investigate some criminal defense lawyers by conducting a raid at his/her office.