Lynch's story -- including his cooperation with local officials, his inability to discuss the medical use of marijuana at his trial, and the regretful jurors -- is reminiscent of the case against Ed Rosenthal, who grew marijuana for patients under an arrangement with the city of Oakland. Rosenthal was convicted on federal drug charges in 2003 and again in 2007, after an appeals court overturned the first verdict because of juror misconduct.

Like Wu, U.S. District Judge Charles Breyer, who presided over Rosenthal's case, refused to allow any explanation of the defendant's motivation, since federal law recognizes no legitimate use for marijuana. And like Lynch, Rosenthal faced a mandatory minimum sentence of five years. But in a surprising turn, Breyer sentenced Rosenthal to one day, which he had already served.

Breyer's leniency was based on his conclusion that Rosenthal had honestly and reasonably believed he was acting within the law. Thus Breyer essentially took into account at sentencing the defense he had not allowed during the trial.

Breyer's legal rationale was a "safety valve" provision that allows departures from the five-year mandatory minimum sentence for growing or distributing more than 100 kilograms of marijuana. This provision applies to cooperative defendants with minimal or no criminal histories who do not possess a firearm, threaten or commit violence, cause death or serious injury, or play a "leadership role."

Since Lynch had employees at his dispensary and was convicted of conspiracy, meeting that last criterion might be tricky, but otherwise he seems to qualify. In Rosenthal's case, the federal appeals court implicitly approved the one-day sentence in a footnote to its decision ordering a retrial.

Unlike Rosenthal, who faced a vindictive Justice Department that unsuccessfully challenged his sentence and then tried to pile on new charges in his second trial, Lynch faces a Justice Department that ostensibly understands the merits of federalism in this area. Assuming Obama is serious about letting states set their own medical marijuana policies, there will be no one to second-guess Wu if he finds a way to keep Lynch out of prison.