This US election is the most important since 1932, when Franklin Delano Roosevelt became president in the depths of the Depression. With much trial and error, FDR saved democracy, at home and abroad. The re-election of Donald Trump would undo much, if not all, of that legacy. Yet his defeat would not end the danger. If that is to happen, American politics has to be transformed.

This election is so important, because the US plays a unique role in the world. It has long been the paramount model of a functioning liberal democracy, leader of the countries that share these values and an essential player in resolving any big global challenge. The re-election of Mr Trump would signify a rejection of all three roles by the American people. No other country or groups of countries is able to take its place. The world would be transformed — and not at all for the better.

During a radio broadcast on 29 December 1940, FDR referred to his country as “the arsenal of democracy”. This was accurate in its implications for the supply of materiel in the second world war. American resources were vital in ensuring victory. But the US offered far more than just might. It proved that it was possible for a great power also to be a law-governed democracy. It was the most potent republic since Rome and provided a model of what such a power could now be. Its example of individual freedom and the democratic spirit shaped the aspirations of billions.