No pot smokers allowed in the U.S.

I was aware that very minor drug infractions could prevent people from getting a U.S. visa, but I was not aware until now that merely admitting that you had, at some point in your life, tried marijuana, was enough to deny a visa and ban you from the United States for life.
From this article in today’s Philippine Star by Michael J. Gurfinkel (an immigration attorney):

Many Filipinos consulted with me regarding the same problem: their visa was denied by the US Embassy because they admitted to the doctors at St. Luke’s that they had, years ago, smoked marijuana or used some other drug. At their visa interview, they are shocked to find that their visa is being refused, with the annotation “you have admitted to committing acts which constitute a controlled substance violation – no waiver.”
In one case, a 29-year-old nurse had been recruited for a job in a US hospital. During visa processing, she was asked a very routine question: “Have you smoked marijuana or taken any controlled substance?” The nurse said that she had “tasted” marijuana once during a party when she was 18 years old. It was just a harmless “try”, done out of curiosity. Her visa was denied, and she was banned for life.

Brutal. OK, the nurse was a naif. You never admit to anything that you don’t have to when dealing with a government. But people who admitted previous drug use to their doctors?
I did a little Googling for the law, and sure enough:

any alien convicted of, or who admits having committed, or who admits acts which constitute the essential elements of–
(I) a crime involving moral turpitude (other than a purely political offense), or
(II) a violation of (or a conspiracy to violate) any law or regulation of a State, the United States, or a foreign country relating to a controlled substance (as defined in section 102 of the Controlled Substances Act (21 U.S.C. 802)), is excludable.

Note: The law has an exclusion for minor offenses in the case of section I, but not for section II (the part dealing with violation of the Controlled Substances Act).
So don’t admit to smoking pot. You can become President if you’re already a U.S. citizen and have smoked pot, but you can’t get a visa to come here.