In the Washington Post, adapted from his forthcoming book. His essay is eloquent. Here’s some excerpts:

A healthy republic would not be debating whether Trump and his followers seek the overthrow of the Founders’ system of liberal democracy. … As one 56-year-old Michigan woman present at the Capitol on Jan. 6, 2021 explained: “We weren’t there to steal things. We weren’t there to do damage. We were just there to overthrow the government.” …

Trump … has explicitly promised to violate the Constitution when he deems it necessary. That by itself makes him a unique candidate in American history and should be disqualifying.

This kind of open challenge to our democracy was never meant to be addressed by the courts. As the Founders well understood, you don’t serve a subpoena to a would-be tyrant and tell him to lawyer up. Nor was it meant to be addressed by the normal processes of democratic elections. They knew, and feared, that a demagogue could capture the allegiance of enough voters to overthrow the system. That was why they gave Congress, and particularly the Senate, supposedly more immune from popular pressures, the power to impeach and remove presidents and to deny them the opportunity to run again — and not simply because they violated some law but because they posed a clear and present danger to the republic. After Trump’s attempt to overthrow the government in 2020, Congress had a chance to use the method prescribed by the Founders in precisely the circumstances they envisioned. But Senate Republicans, out of a combination of ambition and cowardice, refused to play the vital role the Founders envisioned for them. The result is that the nightmare feared by the Founders is one election away from becoming reality.…

Americans … know he would not respect the results of fair elections if he loses, which is the very definition of a tyrant.

So, why will so many vote for him anyway? For a significant segment of the Republican electorate, the white-hot core of the Trump movement, it is because they want to see the system overthrown. …

Many of Trump’s core supporters insist they are patriots, but whether they realize it or not, their allegiance is not to the Founders’ America but to an ethnoreligious definition of the nation that the Founders explicitly rejected. …

If the American system of government fails this year, it will not be because the institutions established by the Founders failed. It will not be because of new technologies or flaws in the Constitution. No system of government can protect against a determined tyrant. Only the people can. This year we will learn if they will.

While I share much of Kagan’s diagnosis of the danger that Trump and his followers present to our nation’s system of “liberal democracy,” I think Kagan goes too far in depicting the Founders and the Constitution they created as an ideal from which we have fallen and to which we must return. Conversely, one need not go as far as Kermit Roosevelt does in arguing that we must repudiate the Founders in favor of resting our collective national creed solely on the beliefs of Lincoln and the Republican Reconstruction that followed the Civil War. Instead, my view is that if we are going to see a way out of our predicament, it will because we recognize that the Founding and its Constitution, reflecting important Enlightenment values that are worth sustaining and nurturing as we continue to seek human progress, were important respects deeply flawed, including in the institutional structures of democracy that they established. Unlike Kagan, I don’t think we can rely on a hope that the public will be sufficiently virtuous to reject would-be tyrants. Instead, like Madison himself, I think we need to be the architects of institutional arrangements that provide for the ongoing operation of collective self-government given the limited amount of civic virtue that necessarily will exist in society. The problem in my view is that our existing institutions are no longer adequate for the level of civic virtue we currently have, and thus we need institutional reforms (along with efforts to re-cultivate more civic virtue) to bring our system into Madisonian equilibrium. In this sense, Madison had the right idea, but he did not implement it correctly. As good Madisonians, we need to repair the serious flaws in the system he and the other Founders created. I think Kagan regrettably misses this key point.