“I think spying did occur,” Barr said. “But the question is whether it was adequately predicated, and I’m not suggesting it wasn’t adequately predicated, but I need to explore that.”

He later attempted to clarify his statement before lawmakers, saying he was concerned “improper surveillance” may have occurred in 2016 and he was "looking into it."

Trump has long called for a probe into the origins of the investigation of his 2016 campaign and has since seized on Barr's remarks, which Democrats have called for the attorney general to walk back.

"There was absolutely spying into my campaign," Trump told reporters last week. "I’ll go a step further. In my opinion it was illegal spying, unprecedented spying and something that should never be allowed to happen in our country again."