Tuesday night’s presidential debate can best be characterized by two of Donald Trump’s favorite words: it was a “disgrace” and a “disaster.” Our challenge now is to think not just morally or theoretically but also politically, in the way that Trump himself does.

On the morning of the debate, the New York Times exposed his lifetime of trying to turn thoughtful citizens into consumers whose stresses and resentments he could stoke as he opened their wallets. But if many doubted in 2016 that he could win an election with such tactics, there’s no doubting that now. His debate performance signaled once again that his re-election campaign is becoming an attempted coup d’etat.

In 1941, Francis Hackett, literary editor of the New Republic, published the book What Mein Kampf Means to America. This was before the attack on Pearl Harbor, and before most Americans imagined that they would actually go to war. “Right before our eyes, like something on the screen,” he wrote, “the vast social fabric [of the republic] has crumbled. . . . On its ruins, with the speed of a world’s fair, [Hitler] and his confederates have run up a political front of startling and provocative modernity. . . . [His movement’s] hand has been so much quicker than the democratic eye, and for his violence we have so little precedent.”

But there’s a precedent for countering Trump democratically, with a symbolic declaration that could be as potent as his debate performance: the four living former U.S. presidents—Barack Obama, George W. Bush, Bill Clinton, and Jimmy Carter—should come together to announce their shared conviction that Donald J. Trump is a clear and present danger to the republic. That might help to galvanize sustained, widespread democratic organizing not only in the courts and in some states’ election bureaucracies but also among voters and federal workers within the Post Office and the Department of Justice, among other agencies.

One precedent that I have in mind began with the late writer Jonathan Schell’s 1981 bestseller The Fate of the Earth. It may have persuaded influential American strategists, including former Secretary of State Henry Kissinger, to abandon their long advocacy of tactical nuclear-war strategies that, Schell showed, are little better than catastrophes-in-waiting. On January 4, 2007, Schell had the satisfaction of reading an arresting Wall Street Journal column, “A World Free of Nuclear Weapons,” bylined by Kissinger, former Secretary of State George Shultz, former Secretary of Defense William Perry, and former Senator Sam Nunn, calling for abolition of nuclear weapons and for energetic “actions required to achieve that goal.”