WASHINGTON — In their book, “How Democracies Die,” political scientists Steven Levitsky and Daniel Ziblatt write: “How do elected authoritarians shatter the democratic institutions that are supposed to constrain them? Some do it in one fell swoop. But more often, the assault on democracy begins slowly. … The erosion of democracy takes place piecemeal, often in baby steps.”

Our nation is divided in many ways, and one of the most important chasms involves the question of whether President Trump poses a threat to our constitutional foundations. Is he merely a loud-mouthed demagogue, or is he an autocrat-in-the making willing to strike at the underpinnings of republican government?

Those of us fearful that Trump is subverting basic freedoms and the arrangements that sustain them are frequently dismissed as alarmists who fail to recognize the endurance of checks, balances and other circuit-breakers. In this view, asserting that Trump imperils our liberties demonstrates a lack of appreciation for the genius that is the American experiment.

It is certainly true that most of our rights are still intact. We still have free speech and a free press, despite Trump’s assaults on both. After all, I am writing this column and you are able to read it — and to disagree with it if you wish.

The opposition party, moreover, has a good chance of taking over at least one house of Congress in this fall’s elections. At levels below the Supreme Court, judges have blocked many of Trump’s most egregious actions, among them the separation of immigrant children from their parents.

For all of this, one can be grateful. But it is precisely because citizens of enduring republican democracies easily fall into complacency that Levitsky and Ziblatt’s warnings are so pertinent.

Begin with those much-touted checks and balances. Their health depends — as my colleagues Norman Ornstein, Thomas Mann and I argued in our book “One Nation After Trump” — on the willingness of those in the legislative and judicial branches to put their institutional loyalties and their stewardship of the system as a whole above their partisan loyalties.

The opposite is happening in the GOP-led Congress. With the exception of a few Republican elected officials at the periphery, Congress has worked to enable Trump’s abuses (witness the behavior of Rep. Devin Nunes (R-Calif.) to undercut Robert Mueller’s investigation) and to minimize the outrageousness of his conduct.

When Trump revoked former CIA director John Brennan’s security clearance in retaliation for Brennan’s criticism of him (and, as Trump confessed in a Wall Street Journal interview, because he objected to Brennan doing his job in 2016 by probing connections between Trump’s campaign and Russia), the response from most Republicans was pathetic.

Trump’s actions were an abuse of presidential power far beyond anything Republicans used to complain about bitterly during President Obama’s term. They are aimed directly at intimidating critics and interfering with a legitimate investigation. Where was House Speaker Paul Ryan on the issue? When Trump first threatened the security clearances of his critics last month, Ryan shrugged it off and said Trump was “just trolling people.” We still await a robust response from party leaders now that the president has shown he had more than “trolling” in mind.

And long before Trump ran for office, Republicans were eager to change the rules of the game when doing so served their purposes, as Michael Tomasky argued last week in the Daily Beast. Consider just their aggressive voter-suppression efforts and their willingness to block even a hearing for Merrick Garland, Obama’s nominee to replace Justice Scalia.

The list of ominous signs goes on and on: Trump invoking Stalin’s phrase “enemies of the people” to describe a free press; the firing, one after another, of public servants who moved to expose potential wrongdoing, starting with former FBI director James Comey; Trump’s willingness, even eagerness, to lie; his effusive praise of foreign despots; his extravagantly abusive (and often racially charged) language against opponents; and his refusal to abide by traditional practices about disclosing his own potential conflicts of interest and those of his family.

This not business as usual. Yet our politics proceeds as if it is. Slowly, Trump has accustomed us to behavior that, at any other recent time and with just about any other politician, would in all probability have been career ending.

We know what a military coup looks like. But as Levitsky and Ziblatt note, a slow-motion dismantling of rules, norms and expectations can be more insidious because we don’t even notice what’s happening to us.

E.J. Dionne’s email address is [email protected]. Twitter: @EJDionne.

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