Donald Trump has already smoked weed?

Obama didn't try to legalize weed at the federal level but allowed states to legalize it if they wanted, through what we call 'prosecutorial restraint', i.e. simply not prosecuting weed use in states that had legalized it.

Trump's Att'y General, Jefferson Beauregard Sessions, is a famous anti-drug crusader. He (Sessions) could very well decide not to allow states to ignore federal law, which would be the end of marijuana legalization, at least while Trump is in the White House.

Trump doesn't agree that he's a minority president (i.e. minority of the popular vote). Like GW Bush, he is behaving as if he has a huge mandate. That will get him in trouble, but in the meanwhile he may decide that what his voters think is all that's important, not majority opinion in the US. His voters, I'm guessing they aren't big on legalizing pot.

He probably has smoked weed. He probably will not help to legalize it.

Obama was a strong supporter of legalizing weed.

WOW, your mom must be so proud of you!