That really isn't how the system works, or at least is not supposed to work. The government is not supposed to have the power to make things legal or illegal on a whim. You have ballot measures and representatives of the people that are supposed to make those decisions. Now you can argue that there are too many interefering factors at play (lobbyists, courts, etc.)
But pot is hardly becoming legal on a whim. It has been a slow climb through local and state legislation to get anywhere near being legal, and it still has to overcome federal hurdles. It is an interesting change to watch, probably the most fascinating shift since prohibition.