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FBI Director James Comey said Wednesday that it makes him "mildly nauseous" to think his decision to reopen the bureau's investigation into Hillary Clinton's emails just days before the election could have impacted voters, but added he would make the same choice again.

In his most detailed explanation and strongest defense of his actions to date, Comey said it was a choice between “really bad and catastrophic” to inform lawmakers about the discovery of additional Clinton emails found on the computer of former Rep. Anthony Weiner, the husband of Clinton aide Huma Abedin.

Democrats pressed Comey on why he chose to make the renewed investigation public, despite the FBI’s general policy not to comment on ongoing investigations.

“Why didn’t you just do the investigation as you would normally, with no public announcement?” Democratic Sen. Dianne Feinstein asked.

Comey said he had the choice to either “speak” or “conceal.”

“I faced a choice,” Comey said. “And I’ve lived my entire career by the tradition that if you can possibly avoid it, you avoid any action in the run-up to an election that might have an impact, whether it’s a dog-catcher election or president of the United States. But I sat there that morning and could not see a door labeled ‘no action here.’”

He called the decision — which quickly became public — “one of the world’s most painful experiences,” but said making it was the right move.

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"It makes me mildly nauseous to think we might have had an impact on the election. But, honestly, it wouldn't change the decision," Comey said in testimony to the Senate Judiciary Committee.

He said he did not take into account the political impact of the move "because down that path lies the death of the FBI as an institution in America."

Comey sent a letter to lawmakers on October 28 announcing the FBI had reopened its probe into Clinton’s emails.

Clinton has, in part, has blamed her loss on Comey's decision. “If the election had been on October 27, I would be your president,” Clinton said during an appearance Tuesday.

Comey also indicated during his hearing Wednesday that the FBI may be investigating whether any members the agency leaked information related to the Clinton probe.

When asked about statements during the campaign by former New York City Mayor and Trump supporter Rudy Giuliani indicating direct knowledge of the investigation, Comey hinted he was looking into the matter. "I don’t know yet, but if I find out that people were leaking information about our investigations, whether to reporters or to private parties, there will be severe consequences," he said.

Comey is appearing in front of the Senate Judiciary Committee for a routine oversight hearing. But the appearance comes just one day after both President Donald Trump dismissed “phony” ties between his campaign and Moscow, and Clinton partially blamed Comey's handling of the investigation for her stunning loss.

FBI Director Comey was the best thing that ever happened to Hillary Clinton in that he gave her a free pass for many bad deeds! The phony... — Donald J. Trump (@realDonaldTrump) May 3, 2017

...Trump/Russia story was an excuse used by the Democrats as justification for losing the election. Perhaps Trump just ran a great campaign? — Donald J. Trump (@realDonaldTrump) May 3, 2017

Clinton's comments Tuesday spurred Trump to respond on Twitter, calling Comey “the best thing that ever happened to Hillary Clinton” for not prosecuting the Democratic nominee.

White House press secretary told reporters later on Wednesday that Trump "has confidence" in Comey, despite the tweets.

In an appearance before the House Intelligence Committee in March, Comey confirmed the FBI was investigating possible collusion between Russia and Trump’s presidential campaign. U.S. intelligence agencies have concluded Moscow interfered in the 2016 election and hacked emails from the Democratic National Committee and a top Clinton campaign official.

“Was it appropriate for you to comment on one investigation repeatedly, and not say anything about the other?” Democratic Sen. Patrick Leahy asked about how Comey treated the investigation into Trump’s campaign and Clinton’s.

“We treated it like we did the Clinton investigation,” Comey maintained. “We didn't say a word about it months into it, and the only thing we have confirmed so far about this is same thing with the Clinton investigation, that we are investigating.”

The director said he has been interviewed by the Justice Department inspector general as part of the investigation into the FBI’s conduct leading up to the election. Comey said he looks forward to telling more of his side of the story as he continues to draw bipartisan criticism.

During his wide ranging testimony, the FBI head reiterated that he has still seen no evidence into Trump’s claims that President Barack Obama surveilled Trump Tower ahead of the campaign. And he warned of the impact of Wikileaks and said Russia is still attempting to influence U.S. elections.

Comey called Wikileaks “intelligence porn” that simply pushes out information with no regard to how it’s used. He also warned that Russia will likely attempt the same types of interference in the 2018 midterm elections.