James Comey defends Clinton email decision but warns of threat from Russia

• FBI director admits Russian interests are still involved in American politics

• Comey defends decision to reveal Clinton’s emails 11 days before election

FBI director James Comey on Wednesday described Russia as “the greatest threat” to US democracy, but defended his decision to keep secret an investigation into the Trump campaign’s links to Moscow despite revealing details of an inquiry into Hillary Clinton’s handling of classified emails.

Giving evidence to a hearing of the Senate judiciary committee, Comey offered his most extensive explanation to date of the thinking behind his different approaches to the two investigations.

Clinton claimed on Tuesday that Comey’s 28 October letter to leading members of Congress about new emails that had been found damaged voter perceptions of her and cost her the election.

“If the election had been on 27 October, I would be your president,” the former Democratic presidential candidate said.

The discovery of the emails ultimately made no difference to the FBI decision not to press charges over the use of the private server.

Asked about Clinton’s claim that his letter could have swung the vote, Comey said: “This was terrible. It makes me mildly nauseous to think we might have had some impact on the election. But honestly, I wouldn’t change the decision.”

The FBI director said that the discovery in October of a new batch classified emails put him in a near impossible dilemma. He said he had to make a choice between “speak or conceal”: to speak would have been “really bad”, he said; to conceal would have been “catastrophic”. So he chose to speak out.

“One of my junior lawyers asked me: should you consider what you do might help elect Trump as president? I said: not for a moment,” Comey said, arguing that political considerations should never be a factor in such decisions.

Trump responded to Clinton’s comments on Tuesday with a tweet claiming: “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!” – an apparent reference to the bureau’s finding that there was nothing to prosecute in the emails case.

Asked about the criticism on Wednesday, the White House spokesman, Sean Spicer, told journalists: “The president has confidence in the director.”

He was asked repeatedly about the contrast between his decision to break silence on the Clinton email case while concealing the existence of a counter-intelligence investigation into the Trump campaign’s contacts with Russian officials during the election.

Comey said that when he first spoke about the Clinton case, in July 2016, he did so because the investigation had been closed, no charges had been made, and he felt that if the Department of Justice in the Obama administration made the announcement it would lose credibility. The discovery of more emails in October might have changed that decision and represented an important development, he added.

The Trump-Russia counter-intelligence investigation, he argued, was highly classified and was in its “very early stages” by the time of the election.

He confirmed that the inquiry was continuing, and agreed when asked whether it was “fair to say that Russia is still involved in American politics”. He went further, describing Russia as “the greatest threat of any nation on earth, given their intention and their capability” to US democracy.

Asked about Comey’s claim that the Russian government is still involved in US politics, Spicer replied: “I think that’s the view of the FBI. We rely on them and the rest of the intelligence community to provide the president with updates on what they’re learning.”

At his hearing, Comey was peppered with questions about leaks about FBI investigations, and repeatedly stated he could neither confirm or deny.

He made one exception, however. Asked about contacts between FBI staff and Rudy Giuliani, a former New York mayor and current Trump aide, he said: “I don’t know yet, but it’s a matter I’m very, very interested in.”

Comey described in detail the process of discovering Clinton’s emails on the laptop of Anthony Weiner, the estranged husband of top Clinton aide Huma Abedin.

He said that “somehow” Clinton’s emails “were being forwarded to Anthony Weiner, including classified information, by her assistant Huma Abedin”. Weiner was being investigated over an alleged online relationship with a teenage girl.

Republican Chuck Grassley, the chairman of the committee, said that the public’s faith in the bureau had been tested lately. Grassley is pressing for answers about the FBI’s investigation into potential coordination between the Trump campaign and Russia.

Comey disclosed the existence of that investigation when he testified at a congressional hearing in March.

Comey also mounted a strong defence of section 702 of the Fisa Amendments Act of 2008, which allows the NSA to use the Prism program to collect internet communications. And he claimed that half the FBI’s work was now affected by encryption on users’ phones or other devices.