The House of Commons is built for confrontation, with rows of benches facing each other across an aisle. When the original Victorian chamber was blitzed to ashes during the second world war, Winston Churchill was adamant that the antagonistic geometry be preserved in the restoration. He spoke dismissively of the foreign, semi-circular assembly, which “enables every individual or every group to move round the centre, adopting various shades of pink according as the weather changes.”

Churchill was leading a national unity government, but that was a wartime expedient. Normal democratic hostilities resumed as soon as Germany surrendered. MPs might rebel against their whips, or even defect, but it takes a national calamity or international crisis for Labour and Tory leaders to declare themselves on the same side.

Donald Trump’s inauguration later this month isn’t an emergency of that kind, but it makes one more likely. The incoming president respects neither democratic principle nor diplomatic convention. America will still be an essential ally to Britain, but not a reliable one. The relationship will be shaped by petulance, surprise and ultimatum.

That will make the prime minister’s job incredibly difficult. It will also test the official opposition. There is no natural affinity between Keir Starmer, the liberal-left human rights lawyer, and Trump. But doing business with unpalatable partners in the national interest is in his job description. Kemi Badenoch’s challenge, as leader of the country’s oldest-established party of the right, is more subtle. She doesn’t have the pressure of running foreign policy, but she does have a........

© The Guardian