OAKSTERDAM university, a self-proclaimed “cannabis college” in Oakland, California, has been called everything from “the Princeton of Pot” to “the Harvard of Hemp”. Its founder, Richard Lee, has become the public face of the movement to legitimise marijuana. A paraplegic, he uses the drug for medical purposes, which is legal in California and 15 other states and in the District of Columbia. He also runs a dispensary for medical marijuana and sponsored a 2010 ballot measure in California to legalise marijuana completely in small amounts, whether medicinal or recreational. That measure failed narrowly, but the idea of legalisation continues to win converts.

Now, however, Mr Lee is busted, harassed and in danger of federal prosecution. This month, armed federal agents stormed into his house and offices to confiscate plants and documents. Mr Lee now says that, indicted or not, he plans to get out of his marijuana-related businesses.

The raids on his properties are only the most telegenic instances of a much wider federal crackdown that has taken states and counties by surprise. Dispensaries, and even landlords of dispensary-operators, all over California, Colorado and Montana have been getting menacing letters. Many have closed shop. Growers and users are by turns livid and scared. Some have protested. Others have ducked back into the black market, as in the old days before medical marijuana was allowed.

The question is why the federal government is doing this. On the one hand there is a federal law, the Controlled Substances Act, which recognises no exception for medical marijuana and thus considers all use and trade of it criminal. But on the other hand the Obama administration originally signalled that it would not deliberately clash with the states about weed. In the so-called Ogden memo of 2009, the Justice Department advised its lawyers to leave small-beer marijuana enforcement to the states and focus on graver crimes.

But then, last year, the administration issued the Cole memo (these things are named after the deputy attorneys-general who draft them). It seemed, in dense verbiage, to suggest that the Ogden memo had been misunderstood, and that federal prosecutors should indeed go after the cannabis trade, especially if they suspect that serious money is being made.

The overall effect has been to confuse everybody and leave matters entirely at the discretion of individual prosecutors. Thus there are few signs of federal aggression in New Mexico, Rhode Island or Vermont, for instance. Rather, the crackdown appears to be occurring in just six federal districts—the four in California, and those in Montana and Colorado.

To Ethan Nadelmann, the head of the Drug Policy Alliance, which lobbies for an end to the failed “war on drugs”, this suggests that six federal prosecutors may be acting on their own, perhaps even in conflict with the Obama administration. The president, in this scenario, is too afraid to touch anything that looks soft on drugs in an election year and stands weakly by.

States do not like it. Democratic and Republican legislators from five medical-marijuana states have written an open letter to Barack Obama to end the “chaos” and leave this matter to the states. Christine Gregoire and Lincoln Chafee, governors of Washington state and Rhode Island, have asked the federal government to reclassify marijuana from a Schedule I drug (like heroin, say) to a Schedule II drug (like morphine) so that doctors can at least prescribe it safely in certain circumstances. Vermont, Colorado, Hawaii, and Connecticut have joined in the request. Ms Gregoire has already found herself having to veto a medical-marijuana bill she supports for fear that her state employees may be indicted by federal prosecutors. To all the good reasons for drug reform can now be added this classically conservative one: states' rights.