As we take a step back and contemplate the actuality of Donald J. Trump’s nomination as the Republican candidate for president, one aspect of the situation stands out. Virtually the entire political class, Republicans and Democrats, knows Trump’s liabilities in extraordinary detail.

The constitutional structure of American government forces politicians, no matter what their motives, to “feel constrained to say and do the right thing according to the Constitution whether or not they are sincere,” Jeffrey Tulis, a professor of history at the University of Texas, wrote me.

But Trump, according to Tulis, is “unique in that no other previous major party presidential candidate has felt so unconstrained by these constitutional norms.”

In fact, the separation of powers under the Constitution was explicitly designed to prevent the usurpation of power by a political leader appealing to popular passions and prejudices. If the framers saw anything coming, it was exactly this: a demagogue in the true sense of the term, someone with a privileged background pretending to be a man of the people, channeling their grievances. In other words, a Trump-like candidate.