If I become the victim of a barbaric crime someday, please don't name a statute for me. Send flowers instead.

Legislators are understandably hesitant to speak out against proposals named for victims of crime, such as Megan's Law or Jennifer's Law. They fear voters will see their opposition as callous toward the victim and the victim's family. The result is often ill-considered legislation.

So it is with the proposed Matthew Shepard Hate Crimes Prevention Act, which Senate leaders have now attached to the annual defense-spending bill, making it almost certain to become law. Like its House counterpart, which has already passed, the legislation is an exercise in political grandstanding.

To begin with, the bill is a solution in search of a problem. It criminalizes conduct that is already illegal under state law. Indeed, all but a tiny number of states have applicable hate-crimes statutes, so the conduct at issue is already doubly prohibited in most places. And no one claims that states are not enforcing the law; to the contrary, Wyoming prosecutors have been praised for swiftly obtaining life sentences for Matthew Shepard's killers.

The proposal's most significant effect would be to allow federal authorities to reprosecute defendants who have already been acquitted in state courts. This is hardly cause to support the bill; indeed, the U.S. Commission on Civil Rights opposes it for exactly this reason.

Americans learn as schoolchildren that the Constitution's double-jeopardy clause forbids the government from prosecuting them twice for the same offense. What they don't learn is the dual-sovereignty exception - that double-jeopardy protections do not apply to separate sovereign governments. An acquittal in state court therefore does not preclude a federal prosecution, and vice versa.

While there may be good reasons for the dual-sovereignty exception, it has always been troubling. Until fairly recently, however, the opportunities for mischief have been limited, since there were so few federal offenses on the books.

But with the explosive growth of the federal criminal code in the last few decades, this is no longer true. Now we are facing the possibility that federal prosecutors will get a second bite at the apple whenever they don't like the outcome of a state case, or if they sense an opportunity to make headlines.

There is no better place to draw the line than at the politically charged Shepard act. Despite its title, it is not really a hate-crimes bill at all. It does not require that a defendant be inspired by hatred - only that he acted "because of" someone's actual or perceived race, religion, national origin, gender, sexual orientation, gender identity, or disability.

But consider: Rapists are seldom indifferent to the gender of their victims. A thief might target the disabled because they are less able to defend themselves. So these victims are chosen "because of" their gender or disability.

This is not just sloppy draftsmanship. Justice Department officials wanted something susceptible to broad construction, and they have strenuously resisted efforts to tighten the bill's language. They apparently like the proposal's broad sweep because it gives them discretion.

Bill supporters say they are confident that Attorney General Eric Holder will not abuse that discretion. But the statute will be around long after Holder is gone. Moreover, all prosecutors are subject to political pressure. Can anyone seriously contend that prosecutors will never succumb to such pressure?

A century ago, Americans were in the throes of a panic over "white slavery," then a common term for forced prostitution. They weren't entirely wrong: Forced prostitution did exist, though it was not nearly so common as they were led to believe. After some melodramatic posturing, Congress passed the Mann Act of 1910, a broad criminal prohibition on transporting women across state lines for "immoral purposes."

Eventually, the law became a tool for abuse. Among those charged were Charlie Chaplin, Frank Lloyd Wright, boxing champion Jack Johnson, poet George Barker, and University of Chicago sociologist William I. Thomas, none of whom was engaged in forcing women into prostitution. Johnson's "crime," for example, essentially amounted to being a black man with a white girlfriend.

Our criminal-justice system is designed to err on the side of acquittal, which helps ensure that the innocent remain free. The wholesale federalization of crime - of which the vague and misleading hate-crimes proposal is a prime example - is a threat to that principle.