Given what Obama seems to mean by decriminalization, this position is not exactly radical. About a dozen states are said to have decriminalized marijuana, which generally means that possession of small amounts for personal use does not result in arrest and can be punished by a modest fine at worst. Possession is still illegal in almost all of those states, the conspicuous exception being Alaska, where possession of a few ounces in one’s home does not trigger any penalty at all. Possessing more than the limit (usually an ounce), growing marijuana, or selling it remain crimes even in so call decrim states.
Update: Now he says he’s against it.