That is the choice with which Republicans are grappling.

Party insiders have spent weeks trying to rally support for Mr Cruz. But they have struggled to convince donors – particularly from the establishment wing – to swallow his hardline positions and awkward style.

He has a reputation as a troublemaker in the Senate, where he has won few friends even among his own party.

His stock has risen during the past week, however, following a convincing win over the front-runner in the Wisconsin primary on Tuesday.

Ever since, Republican donors have been meeting in fusty clubs in Manhattan or in Florida mansions to see whether they can learn to love the 45-year-old senator from Texas.

One such event was held at the Knickerbocker Club on New York's East Side last week, the traditional home of the city's patrician class.

John Catsimidis, an investor and grocery store owner who attended the event, told The New York Times: “Lots of people are giving him a second look. People are scared of Donald Trump, that’s why.”

That he did not merit a second look earlier in the campaign is easy to understand.

The list of people with a grievance goes back to his college days.