I write today to confess error.

A few months back, pondering the ghastly parlor game of choosing between President Donald Trump and President Ted Cruz, I opted — reluctantly, disbelievingly — for Trump, as the lesser of two dangers.

Yes, the real estate tycoon is a know-nothing, uninterested-in-learning-anything buffoon. Also: a demagogue and a bully whose emotional instability would pose a threat to national security.

But the Cruz alternative, it seemed to me then, was even worse. Cruz is smarter than Trump, more calculating than Trump (which is saying something) and way, way more conservative than Trump.

A Trump presidency, or so I reassured myself, at least offered the prospect of unprincipled dealmaking in the service of what is Trump’s only guidepost: promoting the greater glory of Trump. President Cruz would be as absolutist as Sen. Cruz (R-Tex.), and therefore, from my point of view, the worse president.

As results showed Donald Trump leading in at least six states on Super Tuesday, Sens. Ted Cruz (R-Tex.) and Marco Rubio (R-Fla.) argued that nominating him would be bad for the Republican party. Here are key moments from their speeches following the March 1 races. (Sarah Parnass/The Washington Post)

I was wrong.

Since that column in mid-December, Trump has proved himself to be even less knowledgeable and even more unhinged. His election would constitute a grave threat to American values and, potentially, American democracy.

In January, Sen. Lindsey O. Graham (R-S.C.) likened picking between Trump and Cruz to “being shot or poisoned. What does it really matter?”

Except Graham, like me, has come to the unexpected conclusion that it does. “We may be in a position where we have to rally around Ted Cruz as the only way to stop Donald Trump,” Graham told CBS News’s Charlie Rose as the Super Tuesday returns rolled in.

Was that what Graham was really suggesting, Rose asked the man who had joked, just a few days earlier, about how the safest place to murder Cruz would be on the Senate floor?

Graham: “I can’t believe I would say yes, but yes.”

Senator, I feel your astonishment, and raise it. To take one pending example, you probably wouldn’t have difficulty voting to confirm President Cruz’s Supreme Court nominee. I would.

But my fundamental fear is that giving the reins of government to Trump would be even riskier, exposing the country to more long-lasting danger than a court with multiple Cruz nominees.

Trump on the trail demonstrates scant respect for, and even less knowledge of, constitutional and legal limitations. He wants to “open up the libel laws” — actually, to undo limits imposed by the First Amendment — to make it easier to sue media outlets that dare to criticize him. He threatens those who contribute to his political opponents. “They better be careful, they have a lot to hide,” he warned Chicago’s Ricketts family, which has donated to an anti-Trump super PAC.

He cannot tolerate protesters, ordering his goons to “throw them out into the cold” and expressing his own yearning for even more violent measures: “I’d like to punch him in the face.” He would torture terrorism suspects (“Don’t tell me it doesn’t work — torture works,” he said) and kill their families, notwithstanding that those actions constitute war crimes under U.S. and international law.

You could dismiss this as over-the-top campaign trail rhetoric — or you could worry, as I do, about what a man like this would do in office, with the power of government at his disposal. A former White House chief of staff once told me that the most astonishing aspect of the presidency isn’t how constrained the chief executive is by having to deal with a recalcitrant Congress — it’s how much latitude the president has when it comes to conducting military operations.

Perhaps the military would refuse to follow President Trump’s unlawful orders, as former CIA director Michael Hayden suggested. What about an order — issued in a fit of pique against a foreign critic — that is lawful but crazy?

Trump is Nixon with all of the megalomaniacal willingness to abuse power and none of the crafty realpolitik. He is attracted to strongmen, past and present — unapologetically retweeting a Mussolini quote (“What difference does it make whether it’s Mussolini or somebody else?”) and basking in praise from Vladimir Putin.

Of the Republican speaker of the House, Paul D. Ryan (Wis.), Trump said menacingly, on the night of his Super Tuesday victories, “I’m sure I’m going to get along great with him, and if I don’t, he’s going to pay a big price.”

Space precludes going through all of the outrageous things Trump has said or proposed, or his predilection for flat-out lying when called on these offenses. Suffice it to say that, if Trump is elected, Ryan isn’t the only American who might have to pay a price.

Read more from Ruth Marcus’s archive, follow her on Twitter or subscribe to her updates on Facebook.