It’s a panic button the nation had pushed just twice before in the Constitution’s 230-year history (three times, if you count Richard Nixon’s resignation to preempt his certain removal in 1974).

Yet, in the event, the impeachment of Donald Trump packed all the novelty of a tepid Super Bowl matchup.

Long before Wednesday’s anticlimactic acquittal vote, it was clear Senate Majority Leader Mitch McConnell and his caucus had no stomach for confronting a president who has displayed only contempt for their constitutional role.

The only frisson of suspense — a dispute over whether to subpoena eyewitnesses whose testimony threatened to decisively contradict the president’s own account — fizzled when GOP senators closed ranks to spare Trump (and themselves) that humiliation.

But for Americans who paid little attention to the House impeachment inquiry that preceded it, the Senate trial provided incontestable evidence of Trump’s fundamental unfitness.

Those who sampled the three-week melodrama even sporadically witnessed the president’s retreat from a defense of categorical (if unconvincing) denial to an assertion of unbounded presidential authority. In the end, defenders who initially insisted that Trump had been misquoted or misconstrued were reduced to arguing that even his most flagrant misconduct was beyond the Senate’s jurisdiction.

The nadir may have come when defense lawyer Alan Dershowitz insisted that the national interest and Trump’s political fortunes were so intertwined as to be indistinguishable — a claim of executive license rivaled only by Louis XIV’s reputed assertion (“L’etat c’est moi!”) that he and the French nation he ruled were one and the same.

Even Republicans who voted to acquit him were loathe to excuse the president’s conduct, much less embrace his expansive view of presidential authority.

Sen. Lisa Murkowski, the sometimes-independent-minded Alaskan who fell into line by refusing to call eyewitnesses like former national security adviser John Bolton and acting White House Chief of Staff Mick Mulvaney, nevertheless rejected the president’s spurious claims of innocence.

Murkowski said the president’s conduct had been “shameful and wrong” and that “his personal interests do not take precedence over those of this great nation.”

Tennessee Sen. Lamar Alexander acknowledged that House prosecutors had “proved” that Trump conditioned the release of nearly $400 million in military aid to Ukraine on a promise to pursue investigations of former Vice President Joe Biden and his son. But he joined his Ohio colleague Rob Portman in concluding that what was indefensible was not necessarily impeachable.

Sen. Marco Rubio, the Florida Republican Trump branded “Little Marco” when they clashed in the 2016 presidential primary, seemed even to concede that Trump’s misconduct might meet the constitutional standard for impeachment. But he, too, voted to acquit, reasoning that “because actions meet a standard of impeachment does not mean it is in the best interest of the country to remove a President from office.”

Even Sen. Joni Ernst, R-Iowa, who refused to concede that Trump had been guilty of anything, expressed confidence that he would “think twice” before pressuring another foreign leader the way he had leaned on Ukrainian President Volodymyr Zelensky. (The day before his acquittal, Trump dismissed that wishful conceit, repeating his assertion that his conduct throughout the Ukrainian episode had been “perfect.”)

The admission of fallibility, of course, is foreign to Trump’s nature. So he will spend the next 10 months portraying his acquittal as an exoneration, rather than a failure of nerve by an unprincipled Senate.

Like so many other presidential announcements, this claim is groundless; its endless repetition cannot erase his defenders’ public condemnation of the conduct that precipitated his impeachment.

So even if they lack the courage of their convictions, give Republican senators credit for knowing right from wrong. They may have made a calculated decision to look away from Trump’s malignancy, but they know the tumor they’re ignoring is anything but benign.

Brian Dickerson is the editorial page editor of the Detroit Free Press.