Acting FBI Director Andrew McCabe pledged Thursday to alert the Senate Intelligence Committee if there is any political interference in the bureau’s investigation into possible collusion between the Trump campaign and Russia.

“There has been no effort to impede our investigation to date,” McCabe added, at an annual hearing on worldwide threats. “You cannot stop the men and women of the FBI from doing the right thing, protecting the American people, and upholding the Constitution.”

Ousted FBI Director James Comey was originally set to testify, but McCabe was subbed in after Comey was abruptly fired Tuesday.

McCabe also declined to comment Thursday on whether he ever heard Comey tell President Donald Trump he was not the subject of an investigation.

“I can’t comment on any conversations the director may have had with the president,” McCabe said at the top of the hearing, under questioning from Chairman Richard Burr (R-N.C.).

The question was a reference to Trump’s comment in his letter firing Comey that the ousted FBI director had informed him “on three separate occasions, that I am not under investigation.”