Better late than never. It took eight months for Republicans to wake up to the fact that Donald Trump could make off with the party’s crown. After Marco Rubio’s clinical attacks on Mr Trump last week, the airwaves are suddenly awash with anti-Trump attack ads. But they are almost certainly too late to stop him. That task will fall to Hillary Clinton. It promises to be a spectacle unlike anything we have seen. America should brace for the strangest contest in its presidential history.

All things being equal, the outcome should not be in doubt — Mrs Clinton’s victory. Yet there is nothing remotely equal about America in 2016. All that is solid is melting into air. It was not just the Republicans who misread the Trump threat. Just three months ago, Nate Silver, the guru of election forecasters, stuck to his earlier prediction that Mr Trump had only a 2 per cent chance of taking the Republican nomination. He now puts that at 45 to 50 per cent. That still seems too low.

The bookies, meanwhile, give Mr Trump a one in four chance of becoming the next US president. That may also be too low.