Last June the Supreme Court said regulating interstate commerce can involve seizing marijuana from patients who grow it for their own medical use, even when state law permits such cultivation. If so, it may not seem a stretch to claim that regulating interstate commerce can involve stopping doctors from writing barbiturate prescriptions for terminally ill patients who plan to take lethal overdoses, even when state law permits such prescriptions.

The Bush administration's attempt to nullify Oregon's Death With Dignity Act, the focus of a case in which the Supreme Court heard oral arguments on Wednesday, ultimately depends on that claim. But given how broadly the Court has been reading the Commerce Clause lately, I'm hoping it can avoid the issue.

The direct question posed by the case is whether the Justice Department is correct that the Controlled Substances Act (CSA) prohibits doctors from prescribing drugs to help patients kill themselves "regardless of whether state law authorizes or permits such conduct." Then-Attorney General John Ashcroft issued a directive to that effect in 2001, warning doctors they could lose their prescribing privileges if they assisted suicides.

That interpretation was a reversal of the position taken by Ashcroft's predecessor. In 1997 Ashcroft, then a Republican senator from Missouri, unsuccessfully urged Janet Reno to declare physician-assisted suicide a violation of the CSA.

Reno said the CSA was not "intended to displace the states as the primary regulators of the medical profession, or to override a state's determination as to what constitutes legitimate medical practice." She concluded that "the CSA does not authorize [the Drug Enforcement Administration] to prosecute, or to revoke DEA registration of, a physician who has assisted in a suicide in compliance with Oregon law."

This clash between Reno and Ashcroft cast them in roles that contradicted their political reputations. As a "liberal," Reno should have been comfortable with an overbearing federal government that routinely overrides state policy choices. As a "conservative," Ashcroft should have been keen to maintain the distinction between local and national matters at the heart of our federal system and reluctant to flout the will of Oregon's voters, who approved the Death With Dignity Act in 1994 and again in 1997.

It seems both Reno and Ashcroft bent their principles and the law to fit their personal policy preferences. This is the sort of result-oriented legal reasoning President Bush has promised his nominees to the Supreme Court will eschew.

When it comes to Commerce Clause cases, that will be tough, because the Court's precedents invite unprincipled, ad hoc decisions. Consider the comparison I mentioned before: If a ban on medical marijuana is a legitimate part of a broader regulatory scheme involving interstate commerce, is the same necessarily true of a ban on physician-assisted suicide?

On the one hand, doctors, unlike patients who grow their own marijuana, get paid for their services, making their prescriptions an economic activity that, in the aggregate, may have a "substantial effect" on interstate commerce. Furthermore, the drugs they prescribe, unlike homegrown marijuana, are apt to cross state lines before they're consumed.

On the other hand, only a few dozen patients a year get prescriptions for suicide drugs in Oregon, compared to tens of thousands of medical marijuana users in California who, unlike the Oregonians, consume their drug regularly. Not only are the drug quantities much smaller in Oregon, but the distributors are tightly regulated, making illicit diversion even less likely.

Depending on which factors he chooses to emphasize, a justice could vote to uphold a federal ban on medical marijuana but not a federal ban on physician-assisted suicide, or vice versa. He could vote to uphold both or neither.

Because the rules are so malleable, a justice's analysis is apt to be influenced by his personal views regarding medical marijuana and physician-assisted suicide. Against this all-too-human tendency, a determination not to "legislate from the bench" is meager protection.