Donald Trump has said he was surprised by an FBI raid on his former campaign chairman's home, calling the move "pretty tough stuff".
Agents working for special counsel Robert Mueller searched Paul Manafort's home in Alexandria, Virginia, in the early hours of July 26, carrying a warrant seeking tax documents and foreign banking records.
The US president told a question-and-answer session with reporters at his Bedminster, New Jersey, golf course he "thought it was a very strong signal", adding: "They do that very seldom. I was surprised to see it."
Mr Trump also tried to minimise his relationship with Mr Manafort, saying he ran the campaign only for "a very short period of time".
Mr Mueller has been looking into Russian meddling in the 2016 election and any possible collusion with Trump associates.
He has also incorporated other pending investigations into people close to the president, including Mr Manafort, who has been a subject of a long-standing FBI government corruption investigation focused on Ukraine.
Mr Manafort, who worked for years as a political consultant advising the pro-Russian Party of Regions and its leader, former Ukrainian president Viktor Yanukovych, has denied any wrongdoing, saying his work in Ukraine was open and appropriate.
On Thursday, Mr Manafort dropped a law firm representing him in the Mueller-led investigation, switching to one with expertise in international tax cases - indicating that Mr Manafort expects Mr Mueller to focus on his foreign financial entanglements.