Well, this is big.

Sen. Bernie Sanders has gone and endorsed Senate President Pro Tem Becca Balint in her bid for U.S. Congress. It’s not technically a violation of the unwritten rule against taking sides in a party primary because Bernie’s technically not a Democrat, but still.

It’s not the first time he’s done this, but it is the most impactful. In 2020 he endorsed David Zuckerman over Rebecca Holcombe in the Democratic gubernatorial primary, but he didn’t do so until July 27. The white smoke wafted up the chimney three weeks earlier this time, which is crucial because mail ballots are already in circulation.

I can only speculate on the why. Is this one last shot in the sub rosa contest of ideas between fiercely independent Bernie and loyal Democrats Leahy and Welch? It certainly reads like a power play — a contest to see who really captures the hearts and minds of Vermonters.

The less Machiavellian reading is simply that Sanders sees Balint as an ideological match, and Lt. Gov. Molly Gray as an unacceptably centrist candidate. My guess is that it’s mostly the latter, and the former is the cherry on top.

I don’t think Leahy or Welch will be willing to break the rule for their Chosen One. But I bet they’ll bend it some more by continuing to say nice things about Gray without actually endorsing, and keeping their networks active on her behalf.

That’s a big help, but Bernie’s public support is bigger.

It should produce a surge in donations from Bernie’s massive donor list. And it will cement Balint’s standing in liberal and progressive circles.

There are a couple of things Bernie could do that would make his endorsement even more valuable.

He could go on the stump alongside Balint. He would draw his customary large and enthusiastic crowds. Balint is absolutely capable of firing up those crowds and capturing that Bernie energy on her own behalf.

And he could send fundraising emails to Bernie Nation. If even 0.01% of those millions and millions of people were to donate to Balint, it’d buoy her coffers in the critical last weeks before Primary Day.

If you’re trying to argue that this is less of a big deal than it seems, I’d point you to Gray’s rather churlish reaction. She was, as they say, unavailable for comment but did produce a brief written statement saying “The great thing about our state’s democracy is that it is Vermonters who decide elections.”

Sure, but a lot of Vermonters listen to Bernie Sanders.

The endorsement should blunt Gray’s favorite line of attack: that Balint is somehow a captive of moneyed interests because she hasn’t foresworn Super PAC support as vehemently as Gray has. If Gray attempts to reslice that bologna in future debates, Balint’s reply need be nothing more than “Bernie.”

In sum, this is a significant needle mover. It puts Gray on the back foot. The next mile marker in this road race is July 15, when we’ll get second-quarter campaign finance reports for the Congressional candidates. The books are already closed, so those reports won’t reflect any Bernie bounce in Balint’s bankbook.

I should mention the earnest but under-resourced third candidate in the race. Sianay Chase Clifford might well have laid claim to Bernie’s support, but he is nothing if not a political realist. The Progressive Party can make the ideologically pure endorsement of Chase Clifford and barely anyone will notice, but Bernie wants a progressive ally in Congress. He’s done the math. When you add together their scores for progressiveness and electability, Balint gets a higher total than Chase Clifford. And his preference for Balint over Gray is bigger than his presumed affinity with Chase Clifford.

So yeah, it’s big. It may not be the decisive factor, but I’d rather be Balint than Gray right about now.