One of Donald Trump’s greatest achievements in office was his remaking of the American judiciary with the appointment of three outstanding Supreme Court justices and hundreds of lower court judges who defend the Constitution from the federal bench each day.

But now, with just a few bizarre social media posts, Trump has repudiated that entire legacy.

After the Supreme Court two weeks ago unanimously rejected his request to stop a congressional committee from obtaining his tax returns, Trump blasted the court, using the language of the left-wing critics who question the legitimacy of his judicial appointments. “The Supreme Court has lost its honor, prestige, and standing, & has become nothing more than a political body, with our Country paying the price… . Shame on them!” Trump declared on his Truth Social account – oblivious to the fact that these words could just as easily have been uttered by Senate Majority Leader Charles E. Schumer, D-N.Y., or outgoing House Speaker Nancy Pelosi, D-Calif. If anything, the court’s actions in this case – and the refusal of any Trump judges or justices to embrace his election denial conspiracy theories – prove precisely the opposite: He appointed jurists whose only loyalty is to our laws and our Constitution.

But apparently, loyalty to our laws and our Constitution is not the standard Trump seeks to uphold. Quite the opposite. In a rant without precedent in the annals of presidential rhetoric, Trump called this weekend for the “termination” of the Constitution. “A massive Fraud of this type and magnitude allows for the termination of all rules, regulations, and articles, even those found in the Constitution,” he thundered, adding, “Our great ‘Founders’ did not want, and would not condone, False & Fraudulent Elections!”

This is many things, but it’s not conservatism. Respect for the Constitution and its original meaning is the bedrock of the modern conservative movement – so fundamental that House GOP leader Kevin McCarthy, R-Calif., announced that Republicans will read every word of the Constitution out loud on the floor of the chamber when they take control in January. For someone seeking the Republican presidential nomination to call for the Constitution’s termination is nothing short of heresy. With his latest missive, Trump has embraced a form of secular sedevacantism – the erroneous belief held by some extreme traditionalist Catholics that there is currently no valid pope – arguing that Joe Biden is an illegitimate “anti-president” and that he, Trump, should either be reinstalled in office or a new election should be called. (How this would be accomplished, he does not say.) I’m sorry, but this is bat-guano crazy. It should be rejected and repudiated by every self-respecting conservative.

It’s time for Trump supporters to acknowledge a sad but undeniable truth: Trump is spinning out of control. Yes, his presidency was filled with historic accomplishments, and he was treated unfairly by his critics in Congress and the media. But since the election, something has snapped. He has descended into a spiral of conspiracy theories and personal grievances. He has surrounded himself with the political dregs. He dines with Ye, formerly known as Kanye West, after the rapper made virulent antisemitic comments and Nick Fuentes, a notorious white supremacist – in a meeting that was apparently arranged by Milo Yiannopoulos, a former Breitbart editor who was purged for defending pedophilia. Trump blasts the Supreme Court justices he appointed because they will not do his bidding from the bench. And now, in calling for the termination of the Constitution and his reappointment to the presidency, he’s apparently lost touch with reality.

Fellow conservatives, it’s time to move on – because Trump is unstable, and because he cannot win. With his behavior since losing office, Trump has made himself irreversibly toxic to swing voters. A new Marquette Law School national poll finds that his unfavorable rating has surged to 66% – with about one-third of Republicans and independents now viewing him negatively.

Ask yourself: Why was Democrats’ anti-MAGA strategy so effective in the midterm elections? Because Trump, the supposed branding genius, has irretrievably tarnished his own brand. For swing voters, “MAGA” no longer means all the great Trump policies that a majority of Americans approved of while he was in office. It means election denial, the refusal to graciously concede or preside over a peaceful transition, the incitement of the Jan. 6, 2021, attack on the Capitol – and now his public call to suspend the U.S. Constitution.

But instead of figuring this out, he is doubling down on the insanity. He sees the polls showing that the number of Republicans favoring a 2024 run has declined precipitously and that he is trailing Florida Gov. Ron DeSantis in multiple states. So he is trying to energize his base with red meat. But the more he does so, the more he drives away swing voters and makes himself unelectable.

The question is: Can Trump supporters see what Trump can’t? Democrats have now won three elections running against Trump. Will the GOP let them do it a fourth time? Republicans have a plethora of outstanding leaders who could step in and lead the conservative movement to victory in 2024. Trump is not one of them.

If Republicans nominate this man, they will lose – and they will deserve to.

Follow Marc A. Thiessen on Twitter, @marcthiessen.