“Not anymore, I don’t,” Mr. Giuliani said on CNN’s “State of the Union.” “I did when I came in.

He cited recent allegations that the FBI may have planted a secret informant in Mr. Trump’s campaign, as well as recent comments from Judge T.S. Ellis III expressing skepticism about ties between the financial dealings of former Trump campaign chairman Paul Manafort and potential coordination with the Russian government.

He also said Mr. Trump does still want to sit for an interview with Mr. Mueller.

“He is adamant in wanting to do it, but we’re more convinced as we see it that this is a rigged investigation,” Mr. Giuliani said.