He's in a tough position, same as Obama. On the one hand, enforcing federal laws is his job. Presidents really shouldn't be picking and choosing which laws they'll enforce. It's not in their brief.

On the other hand, you degrade respect for the law when so many people are against its enforcement.

Were I Trump I would propose the end of federal drug laws other than trafficking. Possession is something the states can regulate if they wish, and anyway federal possession statutes are unconstitutional. On a practical level they're grossly unfair and give state prosecutors a lot of extra power, because people can always be threatened with prosecution under federal laws, which carry much tougher sentences in most cases.

But Trump can propose anything he wants. The action has to come from Congress, ultimately.