Has the Republican leadership in the Senate already violated the oath all senators will have to take once — if — they sit to try President Trump? We insert that “if” because, we confess, we reckon it’s no lead pipe cinch the House will vote for impeachment. If it does, though, have the Republicans already violated the oath they’d have to take? And what about the Senate Democrats? Have they already showed their hand?

These questions are in the news because the chairman of the House Judiciary Committee, Jerrold Nadler, is on a tear, alleging the GOP leadership is violating the impartial justice oath they will have to take when the try the impeachment charges. Mr. Nadler himself just presided over a scandal of an impeachment hearing. It gave the bum’s rush to anyone wanting to present exculpatory evidence.

In any event, the House hasn’t even voted to send the articles to the Senate and already the fight is on over the bona fides of the solons themselves. Call it history’s most raucous voir dire, as the preliminary examination of jurors is called. This is a sure sign that Messrs. Nadler & Co. doubt their charges are going to hold up in the saucer of the Senate. So the last of their resorts is to question the integrity of the Senators.

Starting with Mitch McConnell’s statement that he’s coordinating with the White House. Our own view is that Mr. McConnell ought to be coordinating with the White House. There are big issues — whether, say, President Trump ought to testify at his own trial. He doesn’t have to. The burden of proof is solely on the prosecution. Mr. Trump, though, may covet the center ring in this circus.

It’s not just that, though. Mr. Nadler is upset that Mr. McConnell, has said he sees “zero” chance of Mr. Trump being convicted in the Senate (the Sun doesn’t share that estimate). And that the chairman of the Judiciary Committee, Lindsey Graham, has predicted the impeachment will “die quickly” in the Senate. The palmetto potentate has vowed to do everything he can to make it “die quickly.”

One of the problems Mr. Nadler has, though, is that the Democrats aren’t standing on ceremony, either. Senators Warren and Sanders have been plumping for impeachment (and saying the most horrible things about the President). “We have a confession. We have a coverup,” Senator Kamala Harris said as early as last month. Added she: “It shouldn’t take very long, because, I mean, he did it out in the open.”

What’s good for the goose is good for the gander, we say. Our own view is that what matters is not what these solons say before the Senate sits on impeachment, but what they do after they take the oath. The Senate has established the form of the oath as: “I solemnly swear that in all things appertaining to the trial of the impeachment of ________, now pending, I will do impartial justice according to the Constitution and laws: so help me God.”

So technically — and substantively — speaking, the Senators aren’t bound to do that until they take their seats for the trial. At that point, each will have to lay aside his or her previous remarks and prejudgments, faire attention, and give it their best effort. Happens all the time in jury boxes across the land, even if the Senate’s role in impeachment isn’t exactly analogous to what happens in a courtroom.

In 1993, a federal district judge named Walter Nixon, who was being impeached, tried to get the Supreme Court to stick its capacious nose into the Senate’s rules (he objected to some proceedings taking place in a Senate committee, rather than the full body). The Nine reckoned that because the Constitution grants the Senate the “sole” power to try all impeachments, the matter was non-justiciable. Judge Nixon was convicted. Let it be a lesson for Mr. Nadler.

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This editorial has been revised from the early edition to give a clearer description of the concern of Congressman Nadler over the impartiality of the GOP leadership.