FBI Director James B. Comey. (Cliff Owen/Associated Press)

IF REPUBLICANS believe the FBI director is corrupt and political, they should have the gumption to say so. Instead, many have insulted James B. Comey with slimy implications and underhanded threats since Tuesday, when he announced that he would not recommend charges against Hillary Clinton relating to her use of a private email server while secretary of state.

Republican leaders had practically promised supporters that Ms. Clinton would be indicted. Instead, Mr. Comey denounced Ms. Clinton’s judgment but explained that the facts of the case did not conform to the fevered partisan fantasies that have developed around them — did not, in other words, merit prosecution. So GOP leaders decided to attack the fact-finder.

That Donald Trump would claim that “our system is absolutely, totally rigged” and that Ms. Clinton bribed Attorney General Loretta E. Lynch was no surprise. The wild, unfounded accusations were on his usual level of accuracy and responsibility. More disheartening were the responses from GOP politicians who should know better than to impugn the professionalism of the FBI director and his agents, particularly after Mr. Comey’s measured, fact-based presentation.

“This announcement defies explanation. No one should be above the law,” House Speaker Paul D. Ryan (R-Wis.) pronounced , suggesting that Mr. Comey had failed in his responsibility. In fact, Mr. Comey offered plenty of explanation, starting with the facts that investigators found no intentional wrongdoing and only a tiny number of emails on Ms. Clinton’s personal account containing information marked classified at the time. In reality, Mr. Comey pointed out, “no reasonable prosecutor would bring such a case.”

Sen. Kelly Ayotte (R-N.H.) claimed that Ms. Clinton “gets to play by a different set of rules than everyone else” before accusing the FBI of “failing to enforce the law.” In fact, as Mr. Comey reported, the FBI could find no case in which anyone has been charged under these circumstances. If the government were to charge her, prosecutors would in effect hold Ms. Clinton to different rules than everyone else.

Sen. Charles E. Grassley (R-Iowa) issued a veiled threat to Mr. Comey: “If it wants to avoid giving the impression that the FBI was pulling punches,” he said, “the agency must now be more transparent than ever in releasing information gathered during its investigation,” presumably so that he and other Republicans can transfigure new details into fresh “proof” of criminality. Not to be outdone, Rep. Jason Chaffetz (R-Utah) will haul Mr. Comey before the House Oversight and Government Reform Committee for a grilling Thursday.

Several other Republicans, meanwhile, called for a new investigation and an independent counsel. As with Benghazi, their motto seems to be: Keep investigating until we get the outcome we want.

“It appears damage is being done to the rule of law,” Mr. Ryan said. He’s right, but the FBI director isn’t doing the damage. The wreckers are those who cast baseless aspersions on U.S. law enforcement in the service of their partisan goals.