It depends on how vicious the US president is at the time, I can see it going back and forth.

The reason I say that is pot already was decriminalized here in canada and would have stayed that way if marc emery hadn't done his "summer of legalization" rally thing.
He brought to much attention to it and pissed off the DEA, and now its back to being illegal.

If it were decriminalized again and everyone just acted cool about it I think it would stay for a while...in Canada anyways.