WASHINGTON (AP) — Republican lawmakers on Wednesday confronted former FBI Director James Comey about his oversight of the Trump-Russia investigation during a politically charged hearing that focused attention on problems with a probe that have becoming a rallying cry for supporters of President Donald Trump.

Comey, making his first appearance before Congress since a harshly critical inspector general report on the investigation, repeatedly said he had been unaware of major problems with each of four applications the FBI submitted in 2016 to 2017 to eavesdrop on a former Trump campaign aide. He said he had been overly confident that the surveillance process was working as it should. He noted that the former campaign aide, Carter Page, accounted for just "a slice" of the investigation but that he wouldn't have signed off on the surveillance had he known of the problems.

The questioning of Comey, conducted with the election just weeks away, underscores the extent to which the FBI's investigation four years ago into potential coordination between Trump's campaign and Russia remains front-and-center in the minds of Republican lawmakers, who see an opening to rally support for the president and cast him as the victim of biased law enforcement.

Comey's answers frustrated Republicans, who have seized on the FBI's reliance on Democratic-funded research in applying to a secretive surveillance court for warrants to monitor Page on suspicion that he was a Russian agent. The inspector general report, and documents released in recent months, have raised significant questions about the reliability of that dossier of research.

The FBI nonetheless relied on that document "over and over and over" again even though it was "fundamentally unsound," said the Judiciary Committee chairman, Republican Sen. Lindsey Graham, a loyal Trump ally facing a tough re-election battle of South Carolina.

"What do we do — we just say that was bad, that's the way it goes? Does anybody get fired? Does anybody go to jail?" Graham said, before turning to Democratic colleagues and saying, "If it happened to us, it can happen to you."

Comey was fired by Trump in May 2017, but in the three and a half years since, he has remained a prominent and complicated character for Republicans and Democrats alike. Republicans have joined Trump in heaping scorn on Comey, but Democrats haven't embraced him either, angered by his public statements made during the Hillary Clinton email case that they believe contributed to her loss. The saga of the FBI's role in the 2016 election is the subject of a recent Showtime miniseries, "The Comey Rule."

Democrats lamented the backward-looking nature of the hearing, seeking to make the case that the Russia investigation was valid and that the committee's time could be better spent on other matters.

"Most people think we should be talking about other things, except maybe President Trump," said Democratic Sen. Amy Klobuchar of Minnesota, while Sen. Patrick Leahy described the hearing as a "political errand" for the president.

Comey, the latest high-profile former official from the FBI or Justice Department to testify in Graham's investigation, acknowledged "concerning" and "embarrassing" problems in the handling of surveillance applications.

"I'm not looking to shirk responsibility," Comey said. "I was the director."

The FBI, for instance, did not reveal to the surveillance court that a key source for the former British spy who compiled the dossier, Christopher Steele, had disavowed in an interview with the FBI information that was attributed to him. The FBI also had investigated the same source years earlier over suspected links to Russian intelligence, according to newly released documents. A former FBI lawyer pleaded guilty as part of U.S. Attorney John Durham's ongoing investigation into the Russia probe to altering an email related to the surveillance of Page.

But Comey defended the investigation, which examined multiple contacts between Russians and Trump associates during the 2016 campaign and was opened after a campaign adviser boasted in London that that he had heard Russia had damaging information about Hillary Clinton.

"In the main, it was done by the book, it was appropriate and it was essential that it be done," Comey said.

He later added, "The overall investigation was very important. The Page slice of it? Much less so."

A Justice Department inspector general report did not find evidence of partisan bias and concluded that the investigation was opened for a legitimate reason, but Republican lawmakers have seized on those errors to cast broader doubt on the Russia investigation, and have released a series of declassified documents that they say supports the conclusion of a flawed probe.

That includes information that national intelligence director John Ratcliffe, a former Texas congressman and Trump loyalist, said he has declassified even though he said he does not know if it is true. In a letter to Graham, Ratcliffe said that in late July 2016, U.S. intelligence agencies obtained "insight" into Russian spycraft alleging that Hillary Clinton, the Democratic presidential candidate, had "approved a campaign plan to stir up a scandal against" Trump.

But Ratcliffe added that American intelligence agencies do "not know the accuracy of this allegation or the extent to which the Russian intelligence analysis may reflect exaggeration or fabrication."

Comey brushed aside questions about that document, saying, "I don't understand Mr. Ratcliffe's letter well enough to comment on it. It's confusing...I really don't know what he's doing."

The Senate panel has already heard from Rod Rosenstein and Sally Yates, both former deputy attorneys general, and has scheduled testimony from ex-FBI Deputy Director Andrew McCabe.