I'm not sure which laws those would be however if that's what's required then Congress should do it.
I don't buy the argument that legalization would "encourage" more folks to smoke pot or do more dangerous drugs. Medical Marijuana is legal here in Illinois and I have two conditions that qualify for it. I'm not running out and asking my doctor for a prescription. There are other ways to manage the pain I have and I opt to use those.
If however there comes a point in time where those methods stop working and medical marijuana is the next logical step, I may opt to try it.
I've also seen extracts from marijuana (which do not require smoking) help those with Parkinsons disease stop shaking so much, for example. I think there's any number of treatments that medical marijuana or extracts from marijuana seems to work well with. The problem as I see it is the big drug industry cannot control it and profit highly from it and that may be behind all the efforts to keep it illegal.
Think about it: You can grow it at home, extract methods are published on YouTube that are easy to follow and one doesn't need a "middle man" to grow/harvest/convert it for use. Cut out big pharma and what do we have? A burgeoning cottage industry that literally takes care of itself.
The more I think about it, I don't see the downside to legalization. Tax it, regulate it like tobacco and alcohol and be done with it.
Since the topic was recreational marijuana, the federal laws concerning it might be a start. right or wrong, they are the laws of the land and either need to be validated or repealed if some folks are to have their way. Perhaps Trump will get around to asking lawmakers to start reviewing a lot of laws for constitutionality the way he is having the departments review regulations.
Like Sessions said - he's there to enforce the laws, right or wrong, and if folks don't want that, they need to work to get the laws changed/repealed.