The acquittal yesterday of Roger Clemens of all charges that he had lied to Congress and tried to obstruct an investigation into whether he used steroids is a moment to savor for those who maintain a decent respect for the Constitution. It’s just not every day that an ordinary citizen throws a no-hitter in the courtroom against batters as powerful as the combined might of the Congress and the Department of Justice. The government’s five-years-long pursuit of the great hurler was ended by a jury in just a few hours. The prosecutors, according to the Associated Press, slinked away from the courthouse without comment, and the Justice Department put out a statement claiming, “we respect the judicial process.”

The claim will be met with incredulity, given the Justice Department’s behavior in this case. The whole thing got going in 2008, when the Congress of the United States dragged Mr. Clemens through the mud over allegations of his use of so-called “performance-enhancing drugs.” That was a hearing that never should have happened. It got out of control largely because of a disgraceful performance by Henry Waxman and became an action of Congress against an individual. Yet Congress is prohibited in the Constitution itself from acting against individuals. The prohibition is in Article I, Section 9, which is the part of the Constitution that lists what Congress may never do under any circumstances. One of the things is that it may never pass a bill of attainder.

The reason is that whatever democratic virtue legislatures have, what happens in them is not due process. In the technical sense, Congress didn’t pass a bill against Mr. Clemens. But it held a hearing in which it dragged his name through the mud, and Congress knew it was off the constitutional rails. “If you had 89 players here, I’d feel a lot better about this hearing,” Congressman Christopher Shays said at the time. “But we have just one.” Mr. Waxman tried to extricate himself from the scandal of its own behavior by saying that Mr. Clemens had asked for the hearing, but, as we pointed out at the time, the Constitution doesn’t say Congress may pass no bill of attainder unless someone asks for it. It says Congress may pass no bill of attainder ever.

Congress compounded its error by handing Mr. Clemens over to the Justice Department. It would have been the better part of valor had the Justice Department told Congress to flake off. It couldn’t resist, though, and put him on trial — only to discover, as one might have guessed after the Waxman hearing, that it was a loser of a case. So desperate for a win was the Justice Department that it twice disobeyed the order of the federal judge, Reggie Walton, not to introduce hearsay evidence. If the prosecution were a pitcher, we noted at the time, it would have been ejected from the game for trying to bean the batter.

An infuriated Judge Walton declared a mis-trial. At that point, the government should have gone to the dugout for good. We like the way it was put by our erstwhile baseball columnist, Tim Marchman, who said of Mr. Clemens: “He probably juiced, he probably lied, and he’s probably the greatest pitcher who ever lived. It would be nice if it there were an easy way to separate those things from one another, but there isn’t, and anyway it’s a job for baseball historians, not prosecutors.” The government eschewed that wisdom and retried the case. It failed to reckon that the whole matter had long since stopped centering on the behavior of Mr. Clemens. It was really the government that was on trial, and what happened yesterday is that at the bottom of the 9th, the government struck out.