Attorney General Bill Barr vowed during Senate testimony Wednesday to “reconstruct” the origins of the Russia investigation, saying he specifically wants to learn the extent of the FBI's surveillance of the Trump campaign during the 2016 election.

During a hearing before the Senate Judiciary Committee, Barr was asked by Republican Sen. Mike Lee of Utah how the investigation began and whether there was any improper conduct at the start of the probe. The questioning comes after Barr previously told lawmakers that "spying" occurred against the Trump campaign and that his DOJ is reviewing the investigation's origins.

BARR REVEALS HE IS REVIEWING 'CONDUCT' OF FBI'S ORIGINAL RUSSIA PROBE

Barr's testimony Wednesday suggested that review would zero in on the use of informants and other surveillance.

“Many people seem to assume that the only intelligence collection that occurred was a single confidential informant and a FISA warrant,” Barr said. “I’d like to find out whether that is in fact true. It strikes me as a fairly anemic effort if that was the counterintelligence effort designed to stop a threat as it's being represented.”

Asked if additional campaign figures were under surveillance, Barr said, "These are things that I need to look at."

He added: “And I have to say, that as I’ve said before, the extent that there was any overreach, I believe it was a few people in the upper echelons of the bureau and perhaps the Department, but those people are no longer there.”

Barr also explained that he's working "closely" with FBI Director Chris Wray "on trying to reconstruct exactly what went down.”

Barr noted that the FBI “has been a little bit handicapped in looking back” due to Special Counsel Robert Mueller’s now-closed investigation and the ongoing investigation into alleged abuses of the Foreign Intelligence Surveillance Act by the Justice Department’s inspector general, which is expected to be completed in the coming weeks.

Barr first announced that he was reviewing the origins of the Russia investigation last month, in what was his first congressional hearing after he released his summary of the findings on Mueller’s report. In that document, Barr said the special counsel found no evidence of collusion between members of the Trump campaign and Russia during the 2016 presidential race. Barr also said that the evidence found in Mueller’s investigation was not sufficient to charge the president with an obstruction of justice offense, though Mueller's team did not reach a conclusion on that front.

Barr later faced criticism for that decision from Democrats, as well as complaints that he downplayed the evidence behind the obstruction probe in his initial summary -- those tensions flared repeatedly during Wednesday's hearing. But the hearing also showed Barr is continuing to pursue an internal review of the Russia case itself.

The FBI’s investigation into Russian meddling and potential collusion with members of the Trump campaign during 2016 began on July 31, 2016, and was opened by now-fired FBI senior counterintelligence agent Peter Strzok who served with the bureau’s counterintelligence division.

BARR TESTIFIES 'SPYING DID OCCUR' ON TRUMP CAMPAIGN, AMID REPORTED REVIEW OF INFORMANT'S ROLE

Barr also said last month he would review the FISA warrants issued against former Trump campaign aide Carter Page. The issuance of the FISA warrants relied, in part, on the unverified anti-Trump dossier authored by ex-British Intelligence Agent Christopher Steele, who worked on behalf of Fusion GPS—a firm paid by the Hillary Clinton campaign and the Democratic National Committee through law firm Perkins Coie to do opposition research against the Trump campaign. In the dossier, Steele accused Page of conspiring with Russians. Page was not charged with any wrongdoing.

Sen. John Cornyn, R-Texas, asked Barr Wednesday if the dossier itself could have been “Russian disinformation.” Barr responded that that was “one of the areas” he is reviewing, and said he was “concerned” about it.

Under questioning later from Sen. Josh Hawley, R-Mo., Barr said that to his knowledge, the FBI pursuing a counter-intelligence investigation against a president is unprecedented.

Hawley called FBI officials’ bias against Trump the “real crisis.”

Barr, meanwhile, has faced backlash from congressional Democrats for saying last month that "spying did occur" against the Trump campaign in 2016, referring to the FISA warrants against Page and the use of an FBI informant.

Sen. Sheldon Whitehouse, D-R.I., questioned Barr on his language Wednesday, asking whether his use of the word was “off the cuff.”

“It was actually off the cuff,” Barr said, adding that he was confused when asked last month if he wanted to change his language. “I thought, what’s the issue? I don’t consider it a pejorative.”

Barr went on to say that it was “commonly used in the press” to refer to authorized surveillance, and added: “It’s commonly used by me.”

Justice Department Inspector General Michael Horowitz’s investigation is not only looking into alleged misconduct related to FISA warrants but also is reportedly reviewing the role of Stefan Halper’s work during the Russia probe. Halper, an American professor reportedly connected with British and American intelligence agencies, has been reported as a confidential source for the FBI during the bureau’s investigation into Russian meddling in the 2016 election.