If you'd been caught in possession of marijuana on federal property, you would be looking at federal administrative or criminal penalties. If you were an immigrant, as Sullivan is (though likely you'd be from Mexico rather than the United Kingdom), you'd be looking at loss of your visa.
But since, in our hypothetical, you're a British immigrant, and a former editor of the New Republic, who happens to write the most influential blog that there is, and since many powerful people in law and politics read and follow your work, the United States Attorney will dismiss all charges against you.
One judge, the one facing a non-hypothetical case against Sullivan himself, noted the discrepancy. Because the judge is constrained from saying what he really meant, I'll say it: Ordinary people are FUCKED under our drug laws. Powerful people skate.
That said, I'll praise Magistrate Judge Robert B. Collings for saying it as bluntly as a man in his position could. I'll note that while Sullivan is not a hypocrite on this issue (he's always favored marijuana reform, perhaps because he uses it to combat nausea from anti-HIV medication, or perhaps because he uses it recreationally) he himself hasn't said a word about the special break he got, a break that very few others would have received.
And meanwhile, he and the guests on his blog speak frequently of "the paradox of libertarianism" or "the Eagles of conservatism" or "hope and change" or whatever big government flavor of the month Sullivan favors. Note this: if Sullivan were to be kicked out of the United States, he'd be on the British NATIONAL HEALTH SERVICE, which may offer wonderful anti-HIV therapy, but as Sullivan himself has noted, doesn't offer at all the quality of health care a wealthy and powerful man like Sullivan can receive, if he's willing to pay for it.
Note that I don't blame Sullivan one little bit for taking the break he got, and that I am not accusing Sullivan of hypocrisy, as he's always been consistent on this issue. For that matter I'd have taken the break too. But I wouldn't have been in a position to take it.
UPDATE: From Andrew Sullivan's recent The Conservative Soul: How We Lost It, And How To Get It Back:
There is, in other words, a presumption in the way a government interacts with its own citizens. That presumption is that they will treat each citizen absolutely alike, unless it has a very compelling reason not to. And it is up to the government to prove it has a good reason to discriminate rather than up to a citizen to prove she is equal under the law.
As the post to which I link points out, to the extent Sullivan was discussing the Equal Protection clause of the United States Constitution (purportedly he was), this is a gross, Sesame Street-level oversimplification that's just plain wrong. Different people in different circumstances are treated differently, and receive "discriminatory" outcomes without compelling reason all the time. As Sullivan can now attest with respect to criminal drug charges.
I'm not the only person to have noted that Sullivan turned on a dime with respect to his formerly fawning treatment of the Bush administration as soon as Bush, who had seemingly promised through campaign meetings with people like the Log Cabin Republicans, showed that he was willing to support a federal amendment banning same sex marriage. Where Sullivan had previously advocated the most bloodthirsty prosecution of the Iraq war, he became a dove. Where Sullivan had previously advocated free market economics, he became an embittered New Deal liberal straight out of a Norman Lear 70s sitcom.
It would be pleasing to see Sullivan give the same treatment to the Obama administration, which gently hinted during the campaign at a relaxation of the war on drugs, for its cynicism and hypocrisy. He could do so without mentioning his case at all. I won't hold my breath, but it's the least he could do, with his powerful voice, for the three prosecuted but unconnected losers who shared the docket with Sullivan on the same charge.