Under Biden, the move could wait until the UK worked out how to meet its 2.5% GDP commitment. Not now

It has been one of the few political constants in a turbulent period for British politics: an agreement that defence spending really should increase. But in the second era of Donald Trump, what was a consensual background hum has suddenly become an ear-splitting alarm.

European Nato members, the UK among them, have long been used to US presidents urging them to spend 2% of GDP at a bare minimum, something only a minority of them nonetheless manage.