Having visited countless Republican precincts across the country in the past few months, Frank Luntz, the Republican pollster, likens his party’s mood to the salesmen in David Mamet’s play Glengarry Glen Ross – everyone is desperate to make a sales target they fear they cannot meet.

While the Democratic presidential race draws strength from the exuberance that followed last year’s victory in mid-term congressional elections, the Republican party is caught in a spiral of angst that threatens to pull its presidential candidates down with it.