Just when it seems Donald Trump could not go lower in his quest for the US Presidency, he does. His refusal to say whether he will accept the election result if he loses puts him beyond the pale of democratic integrity. The central principle that distinguishes civilised democracies from less fortunate countries is respect for an election result.

Trump's advisers and his running mate know this if he does not, which is why his advisers have been at pains since the final debate to remind us that close results have often been challenged. Alas, their candidate was not just referring to close or inconclusive outcomes in a crucial district or state, as he later made clear when he declared he would respect the electoral process "if I win".

Trump's mental state as been identified by many watching him as narcissism. His mind cannot accept that he might be wrong or a failure in any sense. When he fails he needs something else to blame. If he loses the election he will not be able to believe it was because most people did not think him the better candidate, he will be convinced in his own mind the election was rigged.

It is hard to know how much harm this might do to America afterwards. He has a large, loyal following receptive to his claims, delusions and excuses no matter how irrational those have become. But US democracy has deep roots, the legitimacy of the next President is unlikely to be shaken by a loser's inability to believe it.