After one Trump presidency and on the eve of another, it is now clear that a once mighty global superpower is allowing its gaze to turn inward, to feed off resentment more than idealism, to think smaller.

Public sentiment – not just the political class – feels threatened by the flow of migrants once regarded as the country’s lifeblood. Global trade, once an article of faith for free marketeers and architects of the postwar Pax Americana, is now a cancer eating away at US prosperity – its own foreign invasion.

Military alliances and foreign policy no longer command the cross-party consensus of the cold war era, when politics could be relied upon to “stop at the water’s edge”, in the famous formulation of the Truman-era senator Arthur Vandenberg.

Now the politics don’t stop at all, for any reason. And alliances are for chumps.