Republican senators have managed to outdo themselves in cowardice — which is quite a feat.

Last week’s Senate vote blocking a national commission to investigate the Jan. 6 insurrection at the Capitol was even more appalling than either of the Senate’s impeachment trial acquittals of former president Donald Trump.

With few exceptions, Senate Republicans shirked their duties at both trials, despite the oaths they took to defend the Constitution, and, in an impeachment trial, to “do impartial justice.” These derelictions were especially apparent in the first impeachment trial. Faced with overwhelming evidence that Trump had used his official powers to try to coerce a foreign nation into aiding his reelection campaign, all but one Republican (Utah’s Mitt Romney) voted to acquit him, even as the senators refused to call witnesses.

They betrayed their oaths again in February, when 43 of the 50 Republican senators voted to acquit Trump of inciting the insurrection, even though he had largely committed his high crime openly, on television and Twitter, and even though the senators themselves were among the victims.

They acquitted him even though they surely recognized, as their own leader, Sen. Mitch McConnell (Ky.), blisteringly said on the floor on Feb. 13 after voting to acquit, that Trump had engaged in a “disgraceful — disgraceful — dereliction of duty." Rather than “do his job,” McConnell said, Trump “watched television happily — happily — as the chaos unfolded,” hoping “to either overturn the voters’ decision or else torch our institutions on the way out.”

Trump breached his duties in both cases, and Senate Republicans thus failed to carry out theirs. But at least then the senators had excuses, however feeble.

With the first impeachment, they faced the momentous decision of whether to remove a president from office — something that has never been done. You can’t blame anyone for feeling trepidation at such a prospect.

The second time around, most claimed they couldn’t convict a former president, even though he had been impeached while in office for acts committed while in office. Constitutional text and history refute that proposition, but you could at least understand one underlying motivation: The usual sanction for an impeachment conviction is removal. Trump was already gone, posed no further threat of committing official abuse, had just lost an election by 7 million votes and stood as unpopular as ever. So, at least the theory went, why bother convicting him just to formally disqualify him from ever holding federal offices to which he’d never be elected?

Those may not have been great excuses, but at least the Republicans had them.

There was no excuse — none — for what they did last week.

They weren’t being asked to remove anyone from office; they weren’t being asked to pass judgment of any sort. They were merely being asked to allow a bipartisan commission to look into what happened on, and led to, Jan. 6.

Even worse: They actually weren’t voting on whether to create a commission; they were voting on cloture — on whether even to allow a vote on the issue. Using the filibuster, a Republican minority refused to allow a majority (which would have included seven Republicans) to hold that vote.

And they did so out of raw political fear, this time without fig leaves. McConnell’s own leadership colleague, minority whip Sen. John Thune (R-S.D.), actually admitted that Republicans feared that the commission’s findings “could be weaponized politically and drug into next year,” a midterm election year.

As for McConnell, he pulled out all the stops. Virtually echoing British Prime Minister Neville Chamberlain’s notorious call to partisanship in the decisive 1940 parliamentary debate over his handling of Nazi aggression — “I have friends in the House” — McConnell shamelessly asked his colleagues to kill the commission bill as “a personal favor” to him.

With that, the Republicans’ policy of appeasing Trump prevailed once again. But if Republicans are worried about what would happen if the public learned more of the truth about Jan. 6, they have only themselves to blame.

After all, they were the ones who acquitted Trump in the first impeachment trial and let him remain in office. They were the ones who stood mute before Jan. 6 as Trump propagated the "big lie" after the election. They were the ones who left open the horrifying prospect of letting Trump hold office again. They are the ones who continue to wish his wrongs away.

They quiver in fear of the man who cost them the presidency and both houses of Congress. As they continue to quake, the “big lie’s” cancer upon democracy grows, with spurious election audits in pursuit of fantasies of fraud, and with some insanely claiming — reportedly including Trump himself — that he’ll be “reinstated” in due course.

Four years of Trump have led to the Republican Party becoming a threat to democracy, a declining sect dominated by crackpots, charlatans and cowards. Of these, it’s the cowards, including the senators who killed last week’s legislation, who bear the most blame.

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