Former New Jersey Gov. Chris Christie (R) defended special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE's probe into Russia's election meddling on Monday, saying that "you can't argue the investigation hasn't been effective so far."

In an appearance at the University of Chicago, Christie said he has repeatedly told President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE that "there’s no way to make an investigation like this shorter, but there’s lots of ways to make it longer."

"He’s executed on a number of those ways to make it longer," Christie said.

Christie's comments come as tensions ramp up between Mueller and his Republican critics, with Trump calling the investigation a witch hunt and calling for an investigation into whether the FBI or Department of Justice surveilled his campaign for political reasons.

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Christie, a former U.S. attorney, vouched for Mueller, calling him nonpartisan, honest and hardworking. He also pointed to the multiple guilty pleas and indictments as evidence that the investigation has been effective.

"I don’t question Bob Mueller’s honesty or his integrity, never have, and having worked with him for years, I still wouldn’t," Christie said.

“If anyone did infiltrate or surveil participants in a presidential campaign for inappropriate purposes, we need to know about it and take appropriate action," Deputy Attorney General Rod Rosenstein said in a statement.

Christie's defense comes as congressional Republicans seek documents related to an FBI informant who met with multiple people in Trump's campaign. Intelligence officials have argued doing so would threaten lives and national security.