In these schemes, the authoritarian becomes a trusted source of information for favored groups, even as he undermines their grasp on truth, and increases his control over them. As divisions widen, people become less able to find common ground on their own, leaving it to the authoritarian to make unilateral decisions, often in violation of people’s basic rights.

As we anticipate the presidency of Donald J. Trump, who has demonstrated authoritarian tendencies, and what it might mean for our freedoms, I’ve noticed among my own support base that some Americans from both sides of the traditional political spectrum are finding common ground on core American ideals. These include the truth that we are all created equal and share an inalienable right to liberty, and the importance of protecting our democracy—especially under Russian assault. This is an encouraging development.

Unfortunately, I’ve also observed committed partisans on the right and the left—even those who share concerns about Mr. Trump—attacking their own and the other side for finding common cause. They attack not the merits of substance, but out of pure partisan animus. It’s as though some Americans find intrinsic value in division and learned little from Mr. Trump’s exploitation of fissures in American society.