WASHINGTON — Attorney General William Barr, defending his decision to order a review of the Trump-Russia probe's origins, told a Senate panel Wednesday that he thinks “spying did occur” by the U.S. government on President Donald Trump’s 2016 campaign.

“For the same reason we’re worried about foreign influence in elections ... I think spying on a political campaign — it’s a big deal, it’s a big deal,” Barr said in response to a question from Sen. Jeanne Shaheen, D-N.H., the ranking member on the Senate Appropriations subcommittee, who had asked why he is looking into the origins of the investigation.

Barr said that he grew up during the Vietnam War when there was spying on anti-war advocates by the U.S. government and that there were rules put in place to ensure there’s an adequate basis for such action.

“I’m not suggesting that those rules were violated, but I think it’s important to look at that. I’m not talking about the FBI necessarily, but intelligence agencies more broadly,” he said.

Shaheen then asked, “You’re not suggesting that spying occurred?”

Barr paused for several seconds and replied, “I think spying did occur,” though he didn’t elaborate.

He said that he’s not launching an investigation of the FBI and is not suggesting there is a problem that’s “endemic” to the agency, but “I think there was a failure among a group of leaders at the upper echelons.”

“I feel I have an obligation to make sure that government power isn’t abused," he added.

Later in the hearing, Sen. Brian Schatz, D-Hawaii, said that Barr's "spying" comment was "unnecessarily inflammatory" and offered the attorney general the chance to rephrase his remarks — because Schatz said "the word spying could cause everybody in the cable news ecosystem to freak out."

"I'm not sure of all the connotations of that word," Barr replied, adding that he could also describe it as "unauthorized surveillance." "I want to make sure there was no unauthorized surveillance."

Barr declined to elaborate when Sen. Jerry Moran, R-Kan., chairman of the panel, asked what the basis was for his remarks.

"There is a basis for my concern, but I'm not going to discuss the basis," Barr said.

“I’m not saying if improper surveillance occurred,” he added later when asked to clarify — saying only that he was “concerned about it” and looking into the situation.

At a hearing Tuesday before a House Appropriations subcommittee, Barr revealed that he is "reviewing the conduct" of the FBI's Russia probe during the summer of 2016, and that the Department of Justice inspector general will release a report on the agency's use of the Foreign Intelligence Surveillance Act process and other matters in the Russia case in May or June.

Trump on Wednesday praised Barr's revelation of the probe into the investigation of his campaign.

"What I'm most interested in is getting started, hopefully the attorney general, he mentioned it yesterday, he is doing a great job. Getting started on going back to the origins of exactly where this all started," he told reporters at the White House. "Because this was an illegal witch hunt and everybody knew it."

The Senate hearing intended to focus on the 2020 budget request comes a day after House Democrats pressed the attorney general on the forthcoming release of special counsel Robert Mueller’s report on the investigation into Russian interference in the 2016 election.

Barr said Tuesday that his original timeline still stands, and that he planned to release the redacted document by mid-April, specifying that he expects it would come out “within a week” and that it will be released to the public.

On Wednesday, however, Barr implied it may not be released until next week.

"I'm landing the plane right now and I've been willing to discuss my letters and the process going forward, and the report is going to be out next week and I'm not going to go into the details until the plane is on the ground," he said when asked by Sen. Chris Coons, D-Del., whether the White House or the president have already viewed the report or were briefed on the report.

He would not respond to questions from Rep. Nita Lowey, D-N.Y., about whether he had shared any additional information from the report with the White House, or whether administration officials had seen the full document.

Barr later clarified during the hearing that before his summary was sent out, “we did advise the White House counsel’s office that the letters were being sent” and while they weren’t given the document in advance, “it may have been read to them.”

Barr reiterated Wednesday before the Senate that after the redacted version of the Mueller report is released to the public, he's "willing to work with the committees."

"I intend to take up with the House and Senate Judiciary committees what other areas they feel they have a need to have access to the information and see if I can work to accommodate that," said Barr, who added that the most "inflexible" area under the law would be the grand jury material, suggesting he would not seek to disclose those parts to lawmakers.

Sen. John Kennedy, R-La., asked during the hearing whether "there is material risk that the grand jury material would leak" if such information is provided to Congress.

"I think so," Barr said, adding that that could also be the case with other redacted material.

Asked by Sen. Patrick Leahy, D-Vt., whether he had a conversation with Mueller about why he didn't make a recommendation on the issue of obstruction of justice, Barr said, "Yes, I did," and added that there would be a fuller explanation of that conversation in the report.

Barr added, while being questioned by Sen. Chris Van Hollen, D-Md., that he didn't know "whether Bob Mueller supported my conclusion" on obstruction.

The attorney general also declined to say whether he views the Mueller investigation as a "witch hunt," or illegal, as Trump has characterized it.

"It really depends on where you're sitting," Barr said, adding that if someone is falsely accused of something, it could be viewed as a witch hunt. "It is what it is."

Asked Tuesday whether Mueller or anyone on his team reviewed his summary of the report in advance, Barr told the House panel that Mueller's team "did not play a role" in drafting that document and that he did give Mueller an opportunity to review it, but he "declined."

House Democrats had given Barr until April 2 to submit the full report to Congress, a deadline that was not met. In response, the House Judiciary Committee last week passed a resolution that authorizes Rep. Jerry Nadler, D-N.Y., to issue a subpoena for the full, unredacted report. It has not yet been issued.