American presidential inaugurations, with all their pomp and splendour, are a rite of passage but not necessarily memorable. A handful stick out for the first words of the new national chief executive — Franklin D. Roosevelt’s, in 1933 in the depths of the great recession, for “The only thing we have to fear is fear itself” and John F. Kennedy’s, in1961, for “Ask not what your country can do for you but what you can do for your country”. Some have grace notes that remain in the mind — as when, in 1977, Jimmy Carter thanked Gerald Ford for all he had done “to heal our country” in the wake of Watergate.

Most have had a feel-good quality, combined with a sense of anticipation, because the US likes to feel good about itself and believes in looking forward not backwards. That was certainly true of Ronald Reagan’s in 1981, a triumph of a new form of conservatism, with Hollywood glamour the icing on the cake; and Barack Obama’s in 2009, reflecting national pride in the election of America’s first non-white president.

The accession of Donald Trump this week simply feels different, less because of the bitterness of the campaign that elected him — though much of that is still palpable — but because no one, including the new president, knows what he will do in office or how he will conduct himself. Governing by Twitter, for example, has no precedent.