The medical marijuana oral argument.

The first report looks good for the federal government on this, as Justice Souter seems dubious about the plaintiffs' argument:

Backers of California's law seem to think "everybody is going to get it from a friend or from plants in the back yard," Justice David H. Souter told the lawyer for the two women. "They're going to get it in the street. Why isn't that the sensible assumption?"

UPDATE: Justice Breyer also seemed unreceptive to the plaintiffs' argument:

Justice Stephen Breyer said supporters of marijuana for the ill should take their fight to federal drug regulators before coming to the Supreme Court, and several justices repeatedly referred to America's drug addiction problems.

But it's important to note that Breyer and Souter have strongly and consistently backed strong deference to the policy choices of the federal government and opposed the enforcement of constitutional federalism. To be principled and consistent, they really should be expected to reject these arguments, as I noted yesterday.

ANOTHER UPDATE: Justice Scalia shows some signs of agreeing with the federal government's position that it may regulate an entire market, even trivial parts of the market that seem quite separated from the ordinary trade in the product that gave rise to the motivation to control it:

Justice Antonin Scalia asked [plaintiffs' attorney Randy] Barnett how his argument of a trivial economic effect from medical marijuana would apply to federal laws protecting endangered species. Those laws ban possession of ivory or eagle feathers without regard to whether a person obtained them through interstate commerce.

"Are those laws likewise unconstitutional?'' Scalia asked.

The 9th Circuit had relied on the notion that the medical use of home-grown marijuana does not interact with the market in marijuana, and Justice Stevens asked a question that seemed designed to pursue this theory:

Stevens asked Barnett how allowing medical use of marijuana would affect the illegal market. The lawyer said it would slightly reduce demand and reduce prices.

"Reduce demand and reduce prices? Are you sure?'' Stevens said.

Barnette seems to have conceded a point that related to a key part of the 9th Circuit's decision, which is why Stevens express some surprise, saying "Are you sure?"

Justice O'Connor is reported as asking whether medical use of marijuana is "something traditionally regulated by states.'' It's hard to tell, without more, which way she may have been leaning by asking this. I'd like to see more of the transcript before speculating any more, but I'll just note that O'Connor's vote is often crucial. Still, from what I've seen so far -- admittedly little -- I think the Court will find the federal government has the power to regulate here.

UPDATE: Marty Lederman at SCOTUSblog predicts the decision for the federal government will be unanimous (though Justice Thomas might conceivably dissent). Lyle Denniston, also at SCOTUSblog, seems to perceive a ray of light for the plaintiffs. I'll read the whole transcript when it's available, but as indicated above, I agree with Lederman.