First, my biases up front: I am a strong proponent of marijuana legalization/regulation and taxation. And as much as I admire most of President Trump's Cabinet appointments, I think that absolutely the worst one is Jeff Sessions.
That understood, Sessions' announcement is consistent with the position that Trump has taken with respect to the DACA issue and is in fact a healthy one for the nation - return the resolution of difficult policy issues to where it belongs, to the Congress.
The modern Presidency has become an imperial one, and that trend reached its zenith with Obama, who didn't even bother to try to appeal to Congress. He simply ruled by fiat that he wouldn't enforce the laws he didn't like. Not the laws calling for deportment of the "dreamers" and not the laws calling for enforcement of marijuana laws.
Selective enforcement of the laws may have its political conveniences, but it makes a mockery of our Constitutional republic.
The power to make the law belongs to Congress, the power to enforce the law belongs to the executive. And when the executive refuses to enforce the law, that is a slap to the peoples' elected representatives.
Now maybe the Congress needs slapping. It has become lazy and hyper-partisan, more interested in bloodsport than the doing of the peoples' business. And now Trump has called their bluff: I can't continue a DACA program that has no legislative underpinnings. If you want to save these folks then pass a law I can sign. And likewise with respect to legal pot - I can't ignore the laws on the books. If those laws are obsolete and disrespectful of the rights of the states, then change them.
Come on, Congress, do the peoples' business. Reach a compromise on immigration reform in exchange for relief for the dreamers. And repeal the insane federal law that equates pot with heroin.