In less than two weeks, our nation will find out whether a president can win office by purposely appealing to only one portion of the American people.

Any candidate goes into a presidential election knowing he or she will not win some votes. There are deep ideological divisions in U.S. politics that would cause some to vote for anyone with a pulse and the proper political creed. (For the hardest-core, the pulse might be optional.)

But it remains important for a prospective president to commit to addressing the whole country, including the portions beyond his or her political reach. This is part of the reason Abraham Lincoln is rightly revered, even though he presided over a bloody, fraternal war. Before the crisis of disunion, he tried desperately to speak across deep differences: “We are not enemies, but friends. We must not be enemies.” And when the conflict came, he doggedly maintained the pretense that America remained a single country with rebellious portions rather than two countries at war. He sought to preserve the mental possibility of eventual reunification.

The commitment I am referring to is not rare in our history, and not always heroic in its application. Despite their flaws and failures, recent Republican nominees — Mitt Romney, John McCain, George W. Bush, George H.W. Bush — attempted to speak across differences and affirmed the metaphysical ideal of national unity. “Sometimes our differences run so deep, it seems we share a continent, but not a country,” said the younger Bush in his first inaugural. “We do not accept this, and we will not allow it. Our unity, our union, is the serious work of leaders and citizens in every generation; and this is my solemn pledge: I will work to build a single nation of justice and opportunity.”

For the first time in my political lifetime, a Republican president, and now candidate for reelection, cannot make that pledge. President Trump has abandoned even the pretense of addressing the whole country. His divisiveness is not an exception to his principles, it is the substance of his appeal.

Our national cleavage may no longer run along the Mason-Dixon Line, but Trump has encouraged geographic conflict. He has attacked “Democrat-run” cities as cesspools of violence and disorder. He has repeatedly threatened their funding over policy disagreements and embraced the sentiment of “let them rot.” The same is true of “Democrat-run” states: New York state has “gone to hell.” California is “going to hell.” Withholding federal aid to fight wildfires and pandemic relief funds has been on the table. “Why should the people and taxpayers of America,” Trump has asked, “be bailing out poorly run states (such as Illinois, as example) and cities, in all cases Democrat run and managed . . . ?”

Think on this a moment: Trump has threatened funds to save lives in states and cities whose leaders he disdains. This is the model of punitive sanctions against hostile countries — not the way U.S. citizens should be treated by their president.

Trump has also fed racial and ethnic divisions. Against all the evidence, he has stereotyped Hispanics as being prone to rape, and Muslim migrants and refugees as being prone to murder. He has consistently defended Confederate monuments and the Confederate battle flag — the remnant symbols of actual secession. In the midst of an overdue national reckoning on racial justice, Trump warned: “If I don’t win, America’s Suburbs will be OVERRUN with Low Income Projects, Anarchists, Agitators, Looters and, of course, ‘Friendly Protesters.’ ” Trump has made one of the most direct appeals to White identity politics since segregation was still the law of the land.

And the president has encouraged a kind of spiritual secessionism, inviting his supporters to regard their opponents as irredeemable traitors, criminals and conspirators. This is one of the most damaging outcomes of conspiracy thinking. When Trump winks at his QAnon supporters, he is not encouraging a belief that democratic leaders are wrong; he is encouraging a belief that they run a satanic, pedophile cult. He is not accusing Joe Biden of being unqualified but of faking the death of Osama bin Laden and orchestrating the murder of everyone in Navy SEAL Team 6.

How is it possible to have civil disagreement or reasonable compromise with people who you believe are the spawn of Satan? A democracy is designed for disagreement; it is destroyed by mutual contempt.

In the late 1850s and early 1860s, there came a moment for many in our country when they began regarding themselves as part of a different nation. This mental secession preceded physical conflict, but was quickly followed by it.

This is precisely what President Trump advocates in 2020: the mental secession of part of America. There is only one adequate response: for Americans to vote as if their nation depends on it.

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