The supporters of Prop 19 tout the measure as a saving grace for California and a civilized gesture of republican responsibility that will draw marijuana out of the shadows and into the state-controlled light of day. Legalizing the cultivation, sale and limited possession of marijuana would, they argue, lessen the financial burden on the state’s judicial and penal systems and raise sorely needed funds through taxation (not to mention that it would weaken the ill-conceived "war on drugs," which devastates lives with lopsided force along lines of class and race). There’s just one little catch: even if Prop 19 passes, marijuana cultivation, possession and sale will still be illegal according to the federal Controlled Substances Act.

In 2009 the Justice Department signaled that it would turn a blind eye to state-compliant medicinal marijuana operations, but Attorney General Eric Holder recently made it clear that activities related to recreational marijuana will continue to be prosecuted. As Holder put it in an October 13 letter to a group of former heads of the Drug Enforcement Administration, who requested that the federal government take legal action to void Prop 19, "We will vigorously enforce the [Controlled Substances Act] against those individuals and organizations that possess, manufacture or distribute marijuana for recreational use, even if such activities are permitted under state law."

Could the Justice Department nullify all the potential boons of Prop 19? No, says Stephen Gutwillig, California director of the Drug Policy Alliance. "The reality is that the federal government has neither the resources nor the political will to undertake sole—or even primary—enforcement responsibility for low-level marijuana offenses in California," he wrote recently. In other words, without assistance from state and local law enforcement, the Justice Department doesn’t have the means to follow through on Holder’s pledge. That might be why Los Angeles County sheriff Lee Baca recently promised to help the feds by continuing to enforce prohibition laws even if Prop 19 passes. Baca’s October 15 announcement may also have been motivated in part by politics, and it seems to have had an effect. Poll numbers on Prop 19, which had been showing support consistently ahead of opposition in recent months, suddenly began shifting in the negative direction.

In a conversation with The Nation, Hanna Dershowitz, attorney for the University of Southern California’s Institute for Creative Technologies and a Prop 19 advocate, called Baca’s statement "alarming and disturbing," and argued that a California court would not accept a charge from his department unless it violated state or local law. "That an officer of the law would state affirmatively that he’s going to choose which laws he wants to enforce… that’s not his job, and that’s not his right," Dershowitz said.

San Francisco-based defense attorney Zenia Gilg made a similar argument, citing People v. Tilehkooh, a California Court of Appeals case in which the court ruled that a probationer who faced a violation-of-probation charge for possessing state-sanctioned medicinal marijuana could not be convicted "because a state judge is not responsible for enforcing federal law," Gilg told The Nation.

Baca, of course, doesn’t think he would have a tough time prosecuting Prop 19 cases. He believes the federal government will file a successful civil suit arguing that Prop 19 comes into a "positive conflict" with federal law, which means that the state law and the federal law cannot coexist without contradicting one another. (According to the Supremacy Clause of the Constitution, when these conflicts crop up, the federal law cannot be limited.)

Gutwillig, Dershowitz and Gilg all told me that they don’t think state legalization of personal consumption would conflict with federal law, since the feds could still attempt to police consumption on their own. Prop 19 might run into trouble, however, when counties attempt to regulate and tax the pot economy. County bureaucrats who try to issue cultivation and distribution licenses, and city councils that try to tax marijuana sales, could arguably be creating a "positive conflict" between local and federal law. The day after Prop 19 passes, Gilg explains, Holder could stroll into a California court, file a suit against the state and ask the court to "enjoin" the enactment, which would suspend the measure’s provisions until the conflict is resolved.

In his letter to former DEA officials, Holder made no explicit mention of Justice Department plans to pursue such litigation. But even if he did file suit, the court would suspend Prop 19 immediately only if it thought that Holder had a good chance of winning. Otherwise, California could reap the benefits of a legalized pot economy during the protracted legal battle.

Dershowitz believes the court would not suspend the proposition because, she argues, the political will is just not there. But Gilg speculates that the prospect of a recreational-use economy might be enough to spur the federal government to action. She also points out that she "still sees the feds prosecuting medical marijuana cases."

Ever since California became the first state to legalize medical marijuana use in 1996, facilities and patients who comply with state law nonetheless have run into trouble with the federal government. (Thirteen states and the District of Columbia have since legalized medical marijuana, and three more are considering the issue this fall.) The closest the Supreme Court ever came to a resolution regarding federal power on this issue came in 2005, when the Rehnquist court decided the case of two patients: Diane Monson, whose home was raided by federal drug enforcement agents, and Angel Raich. Even though no money ever changed hands—Monson grew her own plants, and Raich got her pot gratis from two caregivers—the Court decided that the federal government could still deem the state-sanctioned use of medical marijuana illegal according to its own laws. It did not, however, determine whether the Controlled Substances Act would nullify state provisions for the medical marijuana industry. In other words, the Court told California that it could not keep federal agents from enforcing federal law, but it quietly passed over the issue of whether federal law would quash the state-sanctioned system for regulating medical marijuana. There’s no way to know how the Roberts Court would rule if Holder files a case against Prop 19, or whether the justices would even want to hear the case.

Meanwhile, a number of California cities—including Stockton, Berkeley, Sacramento, San Jose, Long Beach and Oakland—have already put measures on the ballot to set taxes for marijuana sales should Prop 19 pass. In a very Madisonian tone, Lori Ann Farrell, director of finance for the City of Long Beach, explains her support for a measure that will put a 15 percent tax on local businesses that sell recreational marijuana and a $25 per square foot tax on cultivation sites: "We can’t control statewide what the result will be, but we can control how we handle that result." Ignacio De La Fuente, president of the Oakland City Council, put a measure on the ballot that would raise the tax on medicinal marijuana and create a tax for recreational marijuana. "I have to deal with the local issues and let the federal government do whatever they’re going to do," he told The Nation.

Dershowitz is confident that other counties will quickly follow suit. Even if they do not, Gilg points out, Prop 19 would protect shipments between counties where the pot economy is legal. Likewise, Gutwillig does not foresee a chaotic road ahead. "There may be bad actors who jump into the gray zones during the transition," he conceded, "but the implementation itself is going to be quite deliberate."

States have long served as "laboratories of democracy," and this fall Californians have a historic opportunity to embark on an experiment that will ultimately benefit all Americans, pot smokers and abstainers alike. As Prop 19 supporters grapple with the prospect of legal challenges to the law, they should bear in mind that the specter of the Supremacy Clause is no reason to stay home on November 2. The proposal to legalize marijuana in California may be drawing out the tension between our federal and state governments, but this is a tension our noble republic was designed to sustain.