WASHINGTON — The Tea Party’s favorite part of the Constitution — the 10th Amendment, which limits federal power — arrived at the Supreme Court last week. In keeping with the spirit of the times, it came wrapped in the plot of a soap opera.

The amendment has played a starring role in challenges to the recent federal health care legislation. But the justices have not made the task of divining their own views particularly easy.

Their most recent consideration of where Congress’ constitutional power ends came in a case involving the civil commitment of sex offenders.

Now the court has decided to consider what to do about a woman hell-bent on poisoning her best friend.

The woman, Carol A. Bond of Lansdale, Pa., was at first delighted to learn that her friend was pregnant. Bond’s mood darkened, though, when it emerged that her husband was the father.

“I am going to make your life a living hell,” she said, according to her now-former friend, Myrlinda Haynes.

Bond, a microbiologist, certainly tried. On about two dozen occasions, she spread lethal chemicals on her friend’s car, mailbox and doorknob.

Haynes, who managed to escape serious injury, complained to the local police. They did not respond with particular vigor. After checking to see whether the white powder on her car was cocaine, they advised her to have it cleaned.

Federal postal inspectors were more helpful. They videotaped Bond stealing mail and putting poison in the muffler of Haynes’ car.

When it came time to charge Bond with a crime, federal prosecutors chose a novel theory. They indicted her not only for stealing mail, an obvious federal offense, but also for using unconventional weapons in violation of the Chemical Weapons Convention of 1993, a treaty aimed at terrorists and rogue states.

Had she been prosecuted in state court, Bond would most likely have faced a sentence of three months to two years, her lawyers say. In federal court, she got six years.

Bond’s argument on appeal was that Congress did not have the constitutional power to use a chemical weapons treaty to address a matter of a sort routinely handled by state authorities.

She relied on the 10th Amendment, the one so beloved by Tea Party activists. It says that “the powers not delegated to the United States by the Constitution, nor prohibited by it to the states, are reserved to the states respectively, or to the people.”

A unanimous three-judge panel of the federal appeals court in Philadelphia said Bond’s argument was a serious one of “first impression.” Then the court ducked answering the question by saying Bond was not entitled to raise it. Only states, it said, can mount 10th Amendment challenges.

Paul D. Clement, a solicitor general in the administration of President George W. Bush, now represents Bond. He called the idea that Bond lacks standing to challenge the law under which she was imprisoned “startling” and “absurd.”

More broadly, Clement wrote, the Bond case is an instance of an issue that has lately united conservatives, libertarians and liberals. They say there are too many federal crimes, that they are often simultaneously vague and harsh, and that they undermine state authority to maintain public safety.

Clement said his client’s poisonous rampage was not “successful or particularly sophisticated.”

“Domestic disputes resulting from marital infidelities and culminating in a thumb burn are appropriately handled by local law enforcement authorities,” Clement wrote. “Ms. Bond’s assault against her husband’s paramour did not involve stockpiling chemical weapons, engaging in chemical warfare” and the like, he added.

In the appeals court, federal prosecutors embraced the idea that Bond was powerless to attack her conviction on 10th Amendment grounds. But the federal government reversed course in the Supreme Court.

“A criminal defendant has standing to defend herself by arguing that the statute under which she is being prosecuted was beyond Congress’ Article I authority to enact,” Acting Solicitor General Neal K. Katyal told the justices.

Bond has been in prison for more than three years. Given that two sides agree her case was mishandled, the Supreme Court might have summarily reversed the appeals court’s decision. Instead, it will hear arguments in the case in the next few months and probably issue a decision by June.

That means the case of the poisoned paramour, known formally as Bond v. United States, No. 09-1227, will be among the more closely watched this term.