As Matt Welch noted earlier today, Attorney General Eric Holder is promising that the federal government will "vigorously enforce" marijuana prohibition in California if Proposition 19 passes. "Regardless of the passage of this or similar legislation, the Department of Justice will remain firmly committed to enforcing the Controlled Substances Act (CSA) in all states," Holder said in a letter to eight former DEA administrators who have been urging the Obama administration to take a firm stand against the ballot initiative. "We will vigorously enforce the CSA against those individuals and organizations that possess, manufacture or distribute marijuana for recreational use, even if such activities are permitted under state law."

Good luck with that. In 2008, according to the FBI's numbers, there were about 848,000 marijuana arrests in the United States. The feds accounted (PDF) for less than 1 percent of them. The DEA has about 5,500 special agents nationwide, compared to nearly 70,000 local police officers in California. It certainly can make trouble, but it simply does not have the resources to bust a significant percentage of the state's marijuana offenders now, let alone after every adult is allowed to grow his own pot. If the DEA could not block access to medical marijuana under Bush or Obama, what chance will it have after the drug is legal for recreational purposes as well? Not much, says Stephen Gutwillig, California director of the Drug Policy Alliance:

This is 1996 all over again. Naysayers said then that the passage of Proposition 215, California's medical marijuana law, would be a symbolic gesture at most because the federal government would continue to criminalize all marijuana use. Today more than 80 million Americans live in 14 states and the District of Columbia that have functioning medical marijuana laws. All that happened without a single change in federal law. Under our system of government, states get to decide state law. There is nothing in the United States Constitution that requires that the State of California criminalize anything under state law. If California decides to legalize marijuana through the passage of Proposition 19, nothing in the Constitution stands in the way. In fact, Congress has explicitly left to the states wide discretion to legislate independently in the area of drug control and policy. States do not need to march in lockstep with the federal government or even agree with federal law. 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. Well over 95% of all marijuana arrests in this country are made by state and local law enforcement. The federal government may criminalize marijuana, but it can't force states to do so, and it can't require states to enforce federal law.

More on federalism and marijuana policy here.