In 1815, the Swiss-French writer Benjamin Constant, who had lived through the best and worst of the French Revolution, and gone from an admirer to a fierce critic of Napoleon, published a synthesis on liberal politics confidently titled Principles of Politics Applicable to All Governments.

Constant’s life to date had been a pan-European project, nourished by the Enlightenment’s faith in reasoned toleration. Words, of which he was a master (his solitary novel, Adolphe, is the great account of what happens when a relationship between a young man and an older woman moves from lust to love), he held to be the great creative force of liberty. But if words were the vessels of reasoning politics, they could also degenerate into dangerous delirium. A kind of fevered romance, he recognised, was always there to be awakened. “Men are inclined to enthusiasm,” he wrote in the Principles, “or to get drunk on certain words. Provided they repeat these words, the reality matters little to them.”

Were he here right now Constant would, I think, immediately recognise that on both sides of the Atlantic, the anglophone democracies are living through just such a moment of inebriation. In living memory (mine at any rate), the UK and the US have never been more disunited. Fifty per cent of those recently polled in the US approve of the impeachment of President Donald Trump, while an almost equal number disapprove.