The thing about grown-ups is they are supposed to say when enough is enough. Jim Mattis had obviously had enough when he resigned as Donald Trump’s secretary of defence in December. Now the retired general — and the former leading “adult” in Mr Trump’s administration — says he owes a “duty of silence” to the government in which he could no longer serve. Some attribute Mr Mattis’s coyness to the military code of honour — though he retired from the marines two years before Mr Trump picked him. Either way he joins a small army of people who could damage Mr Trump but have chosen not to.

Such self-effacement is only adding to America’s democratic crisis. In the past three years westerners have discovered that their political systems rely less on the sanctity of the law than on the mettle of people in office. This applies as much to unelected officials in the judiciary, the military and the civil service as to elected politicians. It includes democracies with a written constitution, such as the US, and ones that run by convention, such as Britain. It also applies to people who have quit government. The secret to a strong democracy is its norms, not its rules. To paraphrase Edmund Burke, the only thing that is necessary for liberal democracy’s demise is for good people to do nothing.

Mr Mattis is in good company. His recent memoir, Call Sign Chaos: Learning to Lead, was anticipated as a warning about the direction in which Mr Trump is taking the US. In the event, the only president Mr Mattis’s book criticises is Barack Obama (for letting politics trump military strategy). Mr Mattis thought it would be inappropriate to attack a “sitting president”. He also thought he had implied enough about Mr Trump by resigning as Pentagon chief last year. The same applies to Rex Tillerson, Mr Trump’s first secretary of state, who privately described the president as a “f***ing moron” but has largely kept his counsel in public.