How did this shift come about? Was Trump persuaded on the federalist merits of letting states take the lead on setting marijuana policy? Or did Cory Gardner’s hardball tactics of blockading Senate confirmation of DOJ nominees until the White House reversed itself win the day?

Or … did POTUS realize that few things would piss off his least favorite cabinet nominee more than easing off the war on weed? If so, border hawks should start urging Sessions to take a strong “please don’t build the wall” line in public.

To be fair to Sessions, his determination to enforce federal pot laws in states where it’s legal has been overstated. All he said when he rescinded the Obama DOJ’s hands-off policy was that the local U.S. Attorneys in each state should use their discretion in prosecuting offenders. Last month he watered that down further by urging U.S. Attorneys not to bother with “small marijuana cases.” He’s not demanding that the DEA start rounding up potheads in Denver. But even so:

In a phone call late Wednesday, Trump told Gardner that despite the DOJ memo, the marijuana industry in Colorado will not be targeted, the senator said in a statement Friday. Satisfied, the first-term senator is now backing down from his nominee blockade.

“Since the campaign, President Trump has consistently supported states’ rights to decide for themselves how best to approach marijuana,” Gardner said Friday. “Late Wednesday, I received a commitment from the President that the Department of Justice’s rescission of the Cole memo will not impact Colorado’s legal marijuana industry.”

He added: “Furthermore, President Trump has assured me that he will support a federalism-based legislative solution to fix this states’ rights issue once and for all. Because of these commitments, I have informed the Administration that I will be lifting my remaining holds on Department of Justice nominees.”

The last part is big news, if true. A federal law requiring the DOJ to defer to states on marijuana enforcement would go a long way towards destigmatizing the drug; if you’re pro-legalization, or at least pro-decriminalization at the federal level, that’s obviously a major step. (“We may now be seeing the light at the end of the tunnel,” said one prominent Colorado legalization advocate.) It’d also bring President Trump back into line with candidate Trump’s campaign promises. WaPo flagged this short clip from summer 2016 in its story about this today:

Had to ask @realDonaldTrump about #marijuana in light of his alliance with @GovChristie:#9NEWS #COpolitics pic.twitter.com/lK4btIQWuK

— Brandon Rittiman (@BrandonRittiman) July 29, 2016

Marijuana stocks surged on news of the new policy, which is what you’d expect when an industry in perpetual legal limbo gets a jolt towards legitimacy. One obvious question, though: Is Trump serious about this or is it another example of him telling someone (in this case Gardner) what they want to hear when they’re right in front of him, only to reverse himself privately five minutes later? Legalization advocates are cautious:

U.S. Rep. Earl Blumenauer, an Oregon Democrat and the co-founder of the Congressional Cannabis Caucus, called Gardner’s announcement “another head-spinning moment.”

“We should hope for the best, but not take anything for granted,” Blumenauer said in a statement. “Trump changes his mind constantly, and Republican leadership is still in our way.”

The case for optimism here is that this isn’t an out-of-the-blue reversal a la Trump telling Larry Kudlow to take a look at rejoining TPP. The legalization side has a powerful advocate in Gardner, a senator from a swing state and current chair of the NRSC. If Trump were to reverse himself again, presumably Gardner would reinstate his hold on Trump nominees in the Senate. He has leverage to make sure POTUS keeps his promise. The case for pessimism is that congressional compromise on culture-war issues is always hard and this is, after all, a midterm year. Ryan and McConnell might conclude that they have enough problems this fall already that they shouldn’t do anything that might risk alienating senior citizens. Even if it looks like a “let the states decide” bill on marijuana might have 218 votes in the House, Ryan could invoke the Hastert Rule to say that unless a majority of his own caucus supports it, it’s not coming to the floor.

He should consider two things, though. One: Letting the states lead on marijuana is an issue that polls fantastically well. There’s still considerable Republican opposition to legalizing marijuana outright, but a federalist approach that has the DOJ defer to the states on enforcement routinely does supermajority numbers in surveys. The risk of Ryan angering his own base by passing Gardner’s legislation isn’t that great and may even be marginal if Trump is true to his word and backs the legislation, bringing MAGA Nation into line. Two: Because there’s already bipartisan support and Trump seems onboard with the idea, it’s a cinch that some bill like Gardner’s will pass the House next year if Democrats take back the chamber this fall. That being so, why would Ryan let Pelosi have the credit for passing a 70-percent issue when he can do it himself right now? If anything, having the GOP majority pass it now might ease some of the enthusiasm that left-leaning marijuana legalization advocates feel to vote in November.

Exit question: If even Mr Establishment is now singing the praises of weed, how far away can we be from full legalization, realistically?