When Donald Trump described himself as a “very stable genius”, even some of his supporters sniggered. The US president is clearly not a genius in any normal sense of the word. Rex Tillerson, his own secretary of state, is reputed to have described his boss as a “f***ing moron”.

But Mr Trump has a legitimate claim to three other kinds of “genius”: political genius, instinctive genius and evil genius. Moral disgust with Mr Trump means that his opponents are reluctant to credit him with any kind of intelligence or success. But that kind of thinking, while understandable, is also dangerous. It is one reason why the president frequently wrongfoots his opponents.

As Mr Trump pointed out, when making his own immodest claim to “genius”, he achieved something unprecedented in modern American history. He was a complete political outsider who won the presidency on his first attempt. His enemies would point to the current government shutdown to suggest that the president is nonetheless completely unfit to govern. But Trump supporters will respond by pointing to a growing economy, and the passage of the first large-scale tax reform in more than 30 years.