During the campaign and after being inaugurated, Obama said and AG Eric Holder affirmed that policy going forward would be for the Drug Enforcement Administration not to raid medical marijuana distribution or patient cooperatives (I've talked to a lawyer who objects to using the word "dispensaries" since it's the term the drug warriors prefer and it isn't a legally-defined entity) in states that had medical marijuana laws. There were a couple of raids in Calif. shortly after the statement, but you could perhaps attirbute that to Bush holdovers.
The raids today, however, are a clear reversal of that promise. Now Eric Holder did fudge the promise a bit by talking about maybe going after entities that were violating styate law -- but if that's the case there's no reason not to let the state handle it. The West LA raids conducted today were a multi-agency, feds-state-local operation. I presume we'll get some charges filed, but in a surprising number of these cases no charges are ever filed; it's pure harassment and an effort to nullify the law the voters passed and continue to approve.