First off, Obama cannot override the supreme court decision making cannabis schedule 1.
Then there would be the massive unfunding of many programs/agencies/people.
Then again there would the States Rights issue, only now you'd have states who refuse to legalize even tho the federal gov. does. (easily forseen).
You'd need the Supreme court to reverse their original decision (based on Nixon's twisted political presure). And unwrite many laws. ( Not so easy to unwrite/rewrite laws these days).
You'd need to re-educate the population with actual facts about cannabis and not with the disinformation that is being taught in public schools today.
...to be continued.