Every now and then great parties suffer internecine convulsions. It happened to the Democrats during the Reagan years. It also happened to Britain’s Labour Party under Margaret Thatcher. Today, the Republican Party is courting its own banishment with a presidential contest which is pettier and more personal than most. It may be too late to undo the damage before the election in November.

Mitt Romney, who narrowly won his home state of Michigan on Tuesday night, already looks to be damaged goods. The dwindling number of Republicans who see the glass as half full point to the bitter contest between Barack Obama and Hillary Clinton in 2008. In spite of the divisions, Mr Obama united his party and went onto win a sweeping victory. Then he asked Mrs Clinton to become his secretary of state.

Is it possible to imagine President Romney calling on Newt Gingrich or Rick Santorum? It would be a circular firing squad rather than a “team of rivals”. One comparison is with Barry Goldwater, the Republican nominee whose “extremism in defence of liberty” delivered one of his party’s worst defeats in 1964. Mr Goldwater’s nomination followed a bitter struggle with the moderate “Rockefeller wing”, which he said offered an “echo” rather than a “choice”. Another parallel is Ronald Reagan’s potent challenge to Gerald Ford in 1976, from which the sitting president never recovered.