The clash that erupted late Tuesday night between Senator Elizabeth Warren and majority leader Mitch McConnell served at least one purpose: It exposed an anachronism in the Senate’s hidebound rules. McConnell, the Republican leader of the Senate, stopped the Democratic senator from Massachusetts from continuing to speak against the nomination of Senator Jeff Sessions as attorney general, after Senate Republicans determined that she had violated a rule that forbids impugning the integrity or conduct of other senators. Her offense was reading a letter from Coretta Scott King, the widow of Martin Luther King Jr., that criticized Sessions’ civil rights record.

Most of the ferocious fracas that ensued has centered on McConnell. Critics accused him of interpreting the rule in an unusually strict way to shut Warren up. Male senators, many observers noted, have said much ruder things about one another without drawing any sanctions. It took less than 12 hours before Democrats were raising money off the showdown.

But putting aside for a moment McConnell’s flagrant double standard, why should even strong criticism of Sessions be against Senate rules in the first place? Collegiality is a fine goal; so is preventing fistfights, which, according to Senate lore, was the original idea behind the rule Warren violated. But the Senate should carve out an exception to the rules for instances when one of its members has been nominated to a job in the executive branch. In those cases, whatever the say-no-evil rule may accomplish in making the Senate more decorous comes at the cost of a full, frank debate on important nominees.

After all, none of President Trump’s other cabinet nominee have been protected by the same muzzle. Speaking on the floor about a nominee’s strengths and weaknesses is what senators are supposed to do — and usually can.

Sessions has plenty of weakness to talk about. King’s letter detailed his conduct in a 1984 voting fraud investigation that Sessions led in Alabama when he was a prosecutor, which the civil rights leader’s widow called “a shabby attempt to intimidate and frighten elderly black voters.’’ That’s something senators should be talking about, on the Senate floor and in front of the cameras. But they can’t grapple with the more unseemly part of a nominee’s record if they can’t talk about them, and they can’t talk about them if merely raising legitimate criticisms is deemed a violation of Senate rules.