This from The Economist:

The most worrying aspect of a Trump presidency, though, is that a person with his poor self-control and flawed temperament would have to make snap decisions on national security—with the world’s most powerful army, navy and air force at his command and nuclear-launch codes at his disposal.

Betting markets put the chance of a Trump victory at around three in ten—similar to the odds they gave for Britain voting to leave the European Union. Less obvious, but more likely, is the damage Mr Trump will do even if he loses. He has already broken the bounds of permissible political discourse with his remarks about Mexicans, Muslims, women, dictators and his political rivals. It may be impossible to put them back in place once he is gone.