As the Donald Trump presidency approaches its first anniversary, the key question remains: How well can the American system of government cope with the violation of all established conventions? By some measures it has not done too badly. The United States has certainly lost its leadership role among civilised nations, delighted its enemies and dismayed its allies. But life continues – though, as ever, the rich become richer and the poor poorer. The economy even prospers. The very institutional inertia that has frustrated previous presidents now turns out to have certain virtues.