The Attorney General has decided to ignore the Obama-era policy not to prosecute marijuana possession in the states where it has been legalized. This means federal agents will once again treat marijuana as illegal despite it's having been decriminalized in Alaska, Colorado, California, Massachusetts, Nevada, Oregon, Washington, D.C., and Washington state.
Like gun control, this is a federal vs. states' rights matter, but ironically, in this instance, it's the conservatives who want to assert federal law. What a reversal! The conservatives are the ones who clamor for the priority of state law when it comes to gun ownership (for) and abortion rights (against). Their position on state law goes back to the days of slavery. When the federal government threatened to ban slavery, the southern states insisted it was within their rights to own slaves and that the federal government had no right to deprive them of their property. They fought a war over this.
The moneyed interests want to protect their property this time, too. Venture capitalists have invested heavily in marijuana farming and distribution, and the states have much to gain from the new industry. Nevada, for example, expects to make over $100 million in the first two years of its legalized pot.
Really though, it just looks like the Trump administration taking one more shot at Obama's regulations.