FBI Director Christopher Wray said Tuesday that he has no evidence of agents from his organization illegally surveilling Donald Trump’s 2016 campaign, after Attorney General William Barr told a Senate panel last month he was reviewing the matter.

Wray’s hearing in front of the Senate appropriations subcommittee was scheduled to discuss the president’s 2020 budget requests, but some senators seized the opportunity to question Wray about special counsel Robert Mueller’s Russia investigation and Barr’s decision to “look into” the origins of the probe.

Barr told the committee last month that he believed the FBI had been “spying” on Trump’s 2016 campaign, echoing a claim the president regularly makes without evidence. The Trump-appointed attorney general acknowledged at the time that he had “no specific evidence” that the Justice Department had illegally surveilled the campaign, but he said he was “concerned” about it.

Sen. Jeanne Shaheen (D-N.H.) said Tuesday during the committee hearing that she was “very concerned” by Barr’s use of “spying,” which she called a “very loaded word.”

“It conjures a criminal connotation,” Shaheen said. “And I want to ask you ... when FBI agents conduct investigations against alleged mobsters, suspected terrorists, other criminals, do you believe they’re engaging in spying when they’re following FBI investigative policies and procedures?”

Wray responded, “Well, that’s not the term I would use. ... Look, there are lots of people who have different colloquial phrases. I believe that the FBI’s engaged in investigative activity and part of investigative activity includes surveillance activity of different shapes and sizes. And to me, the key question is making sure that it’s done by the book.”

Trump has repeatedly attacked Mueller’s investigation into Russian interference during the 2016 election, calling it a partisan “witch hunt” and at times pointing to the approval of a surveillance warrant on his campaign aide Carter Page.