Barr did not say what "spying" may have taken place, but he seemed to be alluding to a surveillance warrant the Federal Bureau of Investigation obtained on a Trump aide. "We watched it, yes he did say he thought spying occurred, but then he later on said I don't know or think any rules were broken".
Five seconds of silence filled the hearing room after that, and Barr continued: "The question is whether it was predicated, adequately predicated, and I'm not suggesting it wasn't adequately predicated, but I need to explore that".
Barr then told lawmakers that he would launch his own investigation into how the Justice Department opened its probe into Trump campaign ties to Russian Federation, and indicated that he already believed top officials had behaved inappropriately - and McQuade said he was preventing Congress from fulfilling its constitutional duties.
During questioning by senators, Barr said "spying" on President Donald Trump's campaign was carried out by USA intelligence agencies, but he later recharacterised his concerns as focused on "unauthorised surveillance".
This is an interesting development when you consider that President Donald Trump previously claimed, without evidence, that the Obama administration wiretapped Trump Tower during the 2016 campaign. He was mocked by the media.
Supporters of the probe insist that United States officials were acting appropriately and in the public interest by investigating claims over the Trump campaign's engagements with Russian-linked figures. They were spying on - a term I don't particularly like - but on what the Russians were doing.
'I don't trust Barr, I trust Mueller'.
AG Barr, appearing before a Senate panel, did not say what "spying" had taken place.
"I feel that I have an obligation to ensure government power was not abused", Barr said. This was an attempted take-down of a president. "And we beat them, we beat them", BBC News quoted Donald Trump as saying.
Democrats called on Barr to immediately "disavow and retract" his comments, saying "there is no evidence of spying". Barr responded by asking the congressman: "Do you think it's likely that we are gong to prevail?" So do you feel like it carries more weight now when it comes from the attorney general?
Spying on the Trump campaign certainly occurred.
"Because I knew how illegal this whole thing was".
"What they did was treason, what they did was bad, what they did was against our constitution", Trump said without specifying who he was accusing of treason.
Attorney General William Barr has pledged to release next week Special Counsel Robert Mueller's report on Russia's role in the 2016 US election and contacts between Moscow and President Donald Trump's campaign, albeit with colour-coded redactions.
The one possible exception he left open: If the chairmen of the Senate and House Judiciary Committees wanted to see the full report, Barr seems to suggest he would be willing to talk to them about that.