A whole raft of tired assumptions collapsed today. Britain must be realistic about America now – and our so-called ‘special’ relationshipEven more than his first victory in 2016, Donald Trump’s re-election marks a historic disruption. It is a profound moment of change, not just for the United States but for the rest of the world, too. For decades, the US has been the free world’s essential and reliable nation. Not any more. It could even one day become them against us.Trump 2.0 seems certain to put one of the final nails in the coffin of the post-1945 Pax Americana. In reality, that old normality has been disintegrating since at least the Vietnam conflict. George W Bush’s “war on terror” caused more problems than it solved. Barack Obama and Joe Biden were each reluctant to wield America’s big stick, most recently and tragically in the Middle East. Now, though, there is no hiding from the realities.Martin Kettle is a Guardian columnistDo you have an opinion on the issues raised in this article? If you would like to submit a response of up to 300 words by email to be considered for publication in our letters section, please click here.