So far have expectations of Donald Trump fallen during his candidacy for president that a debate in which he threatened to start a criminal prosecution against his opponent was regarded by pundits as a relative success. But Sunday’s debate was overshadowed by the revelation, which first broke on Friday, of a video from 2005 in which Mr Trump boasts of sexual assault.

There have been so many outrages in his campaign, from insults to Mexicans to the suggestion that all Muslims should be banned from entering the US, that his opponents may be surprised anyone was shocked. But the first major poll since the release of the tape showed a strong reaction against him and it seems likely there are many who will now reconsider voting for a candidate who essentially bragged about committing a crime.

For the moment, the most difficult decision rests with Mr Trump’s fellow Republican politicians. Many have already refused to endorse him: there is no living ex-president or presidential candidate, with the exception of Bob Dole, who will put their name to Mr Trump’s campaign. Another swath of Republican politicians signalled a split with Mr Trump over the weekend.