William Barr’s 30-year relationship with special counsel Robert Mueller has given President Donald Trump pause, according to three people who spoke with CNN.

Barr, the president’s pick to replace Jeff Sessions at the helm of the Justice Department, on Tuesday during his Senate confirmation hearing said he and Mueller “were good friends and would be good friends when this was all over,” referring to Mueller’s probe into Russian interference in the 2016 presidential election.

Barr and Mueller first met at the Justice Department during the George H. W. Bush administration. Their wives are close friends who attend bible study together, per Politico, and Mueller was in attendance for the weddings of two of Barr’s daughters.

“I have known Bob Mueller for 30 years,” Barr said. “We worked closely together throughout my previous tenure at the Department of Justice under President Bush. We’ve been friends since. And I have the utmost respect for Bob and his distinguished record of public service. And when he was named special counsel, I said his selection was ‘good news’ and that, knowing him, I had confidence he would handle the matter properly. And I still have that confidence today.”

Barr also told senators Trump knew about their relationship.