So, Weld reasons, why not try to make it happen to Donald J. Trump, too?

That’s the hopeful thought in what otherwise seems to be Weld’s hopeless bid to derail a president whose support among Republicans was 89 percent last month, according to Gallup. Weld is too much a politician to admit publicly that he sees no shot for himself of winning — a Messiah complex lies at the root of many monumental ambitions.

But he’s also wise enough to know that losing well can achieve great things, like bringing down a president who, he said, “regards the law as something to be evaded.” Can that be done between now and Feb. 11, the date of the New Hampshire primary? Weld rests his hopes on two things: New England Republicanism, which remains alive and well despite reports of its demise; and Trump’s trial in the Senate, whose result may not yet be a foregone conclusion.

On the former, note that Vermont, Massachusetts and New Hampshire all have G.O.P. governors, who, like Weld, are relative moderates compared to the rest of the party. New England Republicans can also be fickle in their loyalties, and late to make up their minds: Buchanan was also seen as a nonstarter against Bush Sr. just weeks before the 1992 primary.

On the latter, Weld knows a lot about the impeachment process, having worked on the House Judiciary Committee’s staff as a young lawyer in 1974 as it considered articles against Richard Nixon. Nixon, Weld recalled, “was essentially forced to withdraw from the presidency because he had been caught lying on television to the American people on one topic” — a foothill of a deception compared to Trump’s Karakoram range.

Weld also knows how quickly things can turn in the course of a trial. “Cases don’t look the same at the end as they do at the beginning,” he noted, recalling his prosecutions of public corruption in the 1980s as United States attorney for the District of Massachusetts, where he won 109 convictions in 111 corruption cases. He believes that if four Republican senators join Democrats in voting to call witnesses — Ohio’s Rob Portman could provide the decisive vote — then anything is possible.