After a year of almost weekly revelations about Robert Mueller’s investigation of Donald Trump’s 2016 campaign, even indictments and guilty pleas of campaign officials have grown familiar. It’s not that the special counsel, Mr. Mueller, is crying wolf; it’s that we’ve gotten used to real wolves. Only truly startling developments engage a lot of us.

The F.B.I. search of the office, home and hotel room of Mr. Trump’s attorney Michael Cohen is such a development. It’s historic, even in the lofty context of a special counsel investigation of the president.

This is what we know, in part from Mr. Cohen’s attorney: The United States attorney’s office in Manhattan, acting on a referral from Mr. Mueller, sought and obtained search warrants for Mr. Cohen’s law office, home and hotel room, seeking evidence related at least in part to his payment of $130,000 in hush money to the adult actress Stephanie Clifford, who goes by her stage name, Stormy Daniels. There are reports that the warrant sought evidence of bank fraud and campaign finance violations, which is consistent with an investigation into allegations that the Daniels payment was illegally sourced or disguised. (For example, routing a payment through a shell company to hide the fact that the money came from the Trump campaign — if that is what happened — would probably violate federal money-laundering laws.)

What does this tell us? First, it reflects that numerous officials — not just Mr. Mueller — concluded that there was probable cause to believe that Mr. Cohen’s law office, home and hotel room contained evidence of a federal crime. A search warrant for a lawyer’s office implicates the attorney-client privilege and core constitutional rights, so the Department of Justice requires unusual levels of approval to seek one. Prosecutors must seek the approval of the United States attorney of the district — in this case the office of Geoffrey Berman, the interim United States attorney appointed by President Trump.