Unfortunately, this administration has a history of broken promises when it comes to respecting state medical marijuana laws. They have always given themselves ample loopholes in any guidance so that they can justify desired prosecutions.
> The size and profitability of marijuana businesses will still be a factor prosecutors can consider, but there also must be additional illegal activities for prosecutors to take action.
With enough scrutiny (which we know the Feds have the capacity for), it's trivial to find some regulation that a particular business is violating. And as soon as they have their justification, they'll come down on suppliers and vendors like a ton of bricks, using both the official violation and the federal Controlled Substances Act in the prosecution.
Overall, this announcement is a good sign that they're losing the war on public opinion, and I don't suspect they'll crack down unilaterally. I think they're going after a strategy of containment; disincentivizing the experiment from spreading, as well as preventing bales of cannabis from flowing across state lines (which, in fairness, will certainly happen).
I was corrected a while ago on a different site that the Obama administration has been very two-faced about progressive MJ laws. I don't know if a lot of people are aware of that, I certainly wasn't.
War, marijuana, spying, etc.