It's often innocently assumed that presidents, by virtue of the office they hold, automatically push aside partisanship in the face of national crises. The slaughter at the Tree of Life congregation in Pittsburgh combined with the pipe bombs sent to President Trump's opponents have certainly created such a moment.

But this wishful thinking overlooks the central fact about Trump’s approach to politics: His grip on power depends entirely on splitting the nation in two. Angry division — rooted in race, gender, immigration status, religion and ideology — allowed Trump to become president. Absent a politics of us-versus-them, Trumpism makes no sense at all.

This explains why Trump will sometimes offer presidentially appropriate words of concord ("It will require all of us working together to extract the hateful poison of anti-Semitism," he said at an Illinois rally on Saturday) but almost immediately return to baiting and assailing his enemies and also groups against whom he hopes to court a backlash.

The New York Times's headline in its Sunday print edition was accurate, and it could have been run at so many other times during his presidency: "Trump Makes Call for Unity at Rally, Then Resumes Old Attacks."

And on Sunday afternoon, Trump took to Twitter to ridicule Democratic donor Tom Steyer as "a crazed & stumbling lunatic." Never mind that Steyer was targeted by one of the more than a dozen pipe bombs sent to the president's critics. The tweet came barely 48 hours after Cesar Sayoc, a Florida man whose van was plastered with pro-Trump and anti-liberal messages, was arrested and charged in the mail bombings.

But none of this should have been surprising. Trump took the threats against his foes so lightly that on Friday he tweeted his complaint that “this ‘Bomb’ stuff” — yes, he really used that phrase — had slowed Republican electoral momentum.

The legitimation of group hatred in the interest of electoral success is the goal of Trump's hyping an immigrant "caravan" from Central America (dutifully given extensive coverage by the very same media Trump regularly assails) and the administration's threat to close our southern border. A White House official unapologetically put a partisan spin on what is supposed to be a serious policy, describing Trump's border move as a way "to address the Democrat-created crisis of mass illegal immigration."

The failure of Republican leaders to denounce a president who is devoting himself to ripping us apart reflects a ground-level truth about Republicanism in 2018: The party of Lincoln and Eisenhower has been consumed — temporarily, one devoutly wishes — by a narrow and exclusionary form of identity politics.

The importance of the backlash around race and immigration inside the GOP is a central theme of a timely, careful and data-rich new book on the 2016 election by political scientists John Sides, Michael Tesler and Lynn Vavreck. In "Identity Crisis," they argue that Trump understood what was happening inside the party in a way his rivals did not.

“Trump ignored the many Republicans who criticized him for emboldening fringe white nationalists-and then became the champion of white voters with racially inflected grievances,” they write. “... Trump tapped into beliefs, ideas and anxieties that were already present and even well established within the party. His support was hiding in plain sight.”

As a result, Republican politicians now have an "incentive to run on issues connected to identity as opposed to a traditional platform of limited government." And the authors offer what turns out to be a dead-on description of the campaign we are watching now: "Trump's positions on immigration, Confederate monuments and national anthem protests have proved more popular with Republican voters than have the GOP tax bill or Republican alternatives to the Affordable Care Act."

The truth of that sentence is brought home in the systematic lying by Republican candidates about what their goal of repealing Obamacare would mean in practice.

Normally, calls to end polarization speak of the need to "bring the two parties together" to find "compromises." But these benign bromides are useless when one party thrives on aggravating mistrust, acrimony and fear.

This is not about blaming Trump for the pipe bombs or the synagogue killings. Responsibility falls upon those who undertook these evil actions. But it is undeniable that the president — with the acquiescence and, too often, the support of his party — has heightened ethnic and racial conflict for his own political benefit.

For Trump and his enablers, national unity is not a noble goal but a dire threat to their political well-being.





E.J. Dionne