The conservative judge who convinced Mike Pence he could not overturn the 2020 election has predicted “the beginning of the end of Donald Trump” – the former president who incited the January 6 insurrection but is now trying to return to the White House.

Speaking to the Washington Post, J Michael Luttig also made a common comparison to another notorious former president, Richard Nixon, who resigned in 1974 over the Watergate scandal.

“What Nixon did was just an ordinary crime,” Luttig said, referring to the cover-up of a break-in at Democratic headquarters. “What Trump has done is quite arguably the worst crime against the United States that a president could commit.”

Luttig was a staffer for Gerald Ford, Ronald Reagan and George HW Bush, who put him on the federal bench in 1991. Now 68, he is a retired conservative jurist widely deemed unlucky not to have made the supreme court. He came to national attention last June, when he appeared before the House January 6 committee.

In a televised hearing, using precise and powerful words, Luttig explained why on 4 January 2021 he told Pence he could not do as Trump wished and block certification of Joe Biden’s election win, an argument Luttig also published on Twitter.

Luttig went on to paint a stark picture of America “at war against herself” and warned that a year and a half after the deadly Capitol riot, Trump and his supporters still posed “a clear and present danger to American democracy”.

Another six months on, Trump is in legal jeopardy amid investigations of his election subversion, his financial and campaign finance affairs and his retention of classified records, and a lawsuit brought by a writer who says he raped her, an allegation Trump denies.

But Trump is still the only declared major candidate for the Republican presidential nomination in 2024, dominating polls of the notional field.

In a lengthy profile published by the Post on Tuesday, Luttig said he had seen “ample evidence” of criminal activity and believed Trump would be indicted. He also cautioned that any decision about indicting the former president should consider how it might “split the nation”, given the inevitable “spectacle” of Trump’s fight to beat any charges.

But the Post said Luttig also thought Trump’s political future had been “dealt triple blows … by his recent assertion that parts of the constitution should be ‘terminated’ to return him to office, the criminal referrals by the January 6 committee and the failure of his favored candidates in the 2022 midterm elections”.

Trump made his remark about the constitution in a social media post in December. The Biden White House rebuked him for remarks it said were “anathema to the soul of our nation”.

The January 6 committee made four criminal referrals to the Department of Justice. The justice department investigation of Trump’s election subversion and incitement of the Capitol attack continues.

High-profile Trump candidates were beaten at the polls in November, costing Republicans control of the Senate and, arguably, a healthier House majority.

Luttig, the Post said, saw in the cumulative effect of such factors “the beginning of the end of Donald Trump”. But he added that Trump had not yet been stopped, and it might be down to the courts to do so.

“Donald Trump has proven that the only thing that can stop him is the law,” Luttig warned.