President Donald Trump. Three words that were unthinkable to tens of millions of Americans — and much of the rest of the world — have now become the future of the United States.

Having confounded Republican elites in the primaries, Mr. Trump did the same to the Democrats in the general election, repeating the judo move of turning the weight of a complacent establishment against it. His victory is a humbling blow to the news media, the pollsters and the Clinton-dominated Democratic leadership.

The candidates appeared neck-and-neck in the popular vote, but Mr. Trump bested Hillary Clinton in the Electoral College.

So who is the man who will be the 45th president?

After a year and a half of erratic tweets and rambling speeches, we can’t be certain. We don’t know how Mr. Trump would carry out basic functions of the executive. We don’t know what financial conflicts he might have, since he never released his tax returns, breaking with 40 years of tradition in both parties. We don’t know if he has the capacity to focus on any issue and arrive at a rational conclusion. We don’t know if he has any idea what it means to control the largest nuclear arsenal in the world.