In a major corruption case yesterday, overturning the conviction of former Virginia Governor Robert McDonnell, a unanimous Supreme Court acknowledged that his actions had been “distasteful” or “even worse.” But it also held that the federal government had not deserved to win – at least so far.

The case may be spun as one of prosecutorial overreach or of undue judicial leniency. But the party that most merits the chastisement is Congress.

McDonnell had surely accepted lots of loot (jewelry, wedding parties, cash) from his biggest bankroller—a nutritional supplement huckster—in exchange for lots of favors only a governor could give. These mostly involved things like cajoling state universities to do studies of the fellow’s products or leaning on other officials to do a bit of networking for the huckster about possible state contracts. In the parlance, there were quid pro quos. But the issue was the nature of the quos. As the Court put it, to convict McDonnell a jury had to see evidence that the favor was an “official act,” and the official act had to be something fairly formal and specific that lay within the Governor’s job description—issuing an order, closing a contract, signing legislation, and so on. And here the trial judge did not tell the jurors they needed to find such a thing. Instead, they were allowed to convict McDonnell out of a rough sense that his actions were, well, distasteful or even worse, when they might have been just part of the usual flotsam and jetsam of political influence-peddling.

But the legal problem here was that the laws under which McDonnell was convicted did not contain the term “official act.” They didn’t even contain the term “bribe.”

Here’s the background. There is one federal law, 18 USC section 201 that explicitly condemns bribe-taking by federal officials. But to go after state or local officials the DOJ has to rely on the legal fiction that the official has violated the mail or wire fraud laws (and sometimes the extortion law). The fraud laws are supposed to be about larcenous swindling—as in a Ponzi scheme. But through the 1980s US Attorneys deployed the metaphoric idea that bribe-taking officials “steal” the voters’ entitlement to fair government. Then in a 1987 case called McNally the Supreme Court struck down this idea as a misreading of the fraud statutes. But then Congress, in a sincere but feckless effort to restore the DOJ’s power, responded by enacting the infamous 18 USC section 1346, which makes it a federal  crime to deprive someone of the honest services to which that person is entitled. Yes, that’s a close paraphrase and the law is just that bizarrely fuzzy—although the government must also show that somehow a letter was mailed or a phone call made in the course of the crime, just to ensure federal jurisdiction.

Prosecutors then ran rampant with this law, and defendants attacked it as unconstitutionally vague. In the 2011 case involving Enron’s Jeffrey Skilling (a case involving private, not public corruption, but section 1346 blurs the two), the Court dodged the nuclear constitutional issue by saying that 1346 only applies to bribes or kickbacks, not more inchoate conflicts of interest. But what does a “bribe” mean under section 1346? And a bribe for what kind of act?

So back to McDonnell, who also tried the nuclear option, but again the Court dodged the big issue and decided the case on statutory grounds. Seeking some guidance, and with the agreement of the parties,  the Court borrowed the definitional language of 18 USC section 201, with its relative  clarity about what the “quo” needs to be—see above. Essentially, the Court rewrote section 1346 to make up for the negligence of Congress.

The separate extortion law, 18 USC section 1951, is equally mushy on the nature of the thing the official must do for a payor. Indeed, as construed earlier by the Court, the extortion law is built on yet another legal fiction, because “extortion,” which normally connotes duress or even threats of violence, can occur even if the extortion “victim” acts quite consensually. So the Court incorporated into section 1951 the same rabbit it pulled out of the section 201 hat for the fraud laws.

Section 201 is itself not a model of clarity, especially because it carries with it a lesser included offense of taking or giving “gratuities,” the definition of which is also pretty uncertain.

But at least for federal officials Congress made some effort to tell prosecutors, judges, and juries what the elements of the crime are. Not so under the laws at work in McDonnell.

So what we have seen for decades now has been extreme disparity in interpretations of the statutes by various US Attorneys, probably unjust convictions of fairly innocent, if careless defendants, probably unjust appellate victories by pretty sleazy defendants, and overall a lot of costly waste in the federal legal system. And, finally we have seen a few unsatisfying, if pragmatic, Supreme Court decisions trying to mitigate the mess.

Don’t feel too sorry for McDonnell. He was egregiously greedy and he’ll probably stay out of prison now.  Don’t feel sorry for the prosecutors—they were greedy in their own way (and they may yet get a shot at nailing McDonnell anyway under the new guidance). And feel free to be mad at the Justices for offering lenity to a member of the white collar elite in a legal system rarely showing lenity in applying the broad and vague laws that condemn all the poor defendants. But please reserve a dose of scorn for the Congress that writes absurdities like section 1946.

Robert Weisberg is the Edwin E. Huddleson, Jr. Professor of Law at Stanford Law School and Faculty Co-Director of the Stanford Criminal Justice Center.