It *is* strange that Bernie didn’t use the past two and a half years to declare victory in his struggle to push the Democratic Party towards socialism and re-register as a Democrat. Retaining his independence was useful as a way of signaling that he disagreed fundamentally with the party’s neoliberal establishment on matters like trade and health care. With the early 2020 contenders scrambling to pander to his 2016 base by embracing proposals like Medicare for all, he could have used re-registration to signal that the Democrats’ transformation into a truly progressive party is complete, or at least far enough along to have made socialists a constituency that can no longer be taken for granted.

But he never did get around to it. How come?

One of his advisors told CNN yesterday that Bernie will sign a pledge to run as a Democrat and govern as a Democrat if elected. What that means in practice is unclear. Will Sanders have to re-register, or will it suffice for him to tell people, “Sure, I’m a Democrat, fine,” when asked on the trail?

Sen. Bernie Sanders plans to sign a party pledge affirming that he will run for president as a Democrat in 2020 and serve as one if elected, senior campaign adviser Jeff Weaver told CNN on Wednesday.

The Democratic National Committee said on Tuesday that it planned to meet in the coming week with the presidential primary campaigns and distribute a form to the candidates, who under bylaws agreed on last August will be required “to affirm in writing” that they “are a member of the Democratic Party, will accept the Democratic nomination” and “will run and serve as a member of the Democratic Party.”

“Who cares whether he’s technically a member of the party or not?” you may be wondering. “If Democratic voters deem him enough of a Democrat to nominate him then he’s a Democrat.” Eh, you might be surprised at how much this matters. Ron Brownstein looked at the Hillary/Bernie race of 2016 to see which groups each candidate did best with. Sanders’s core constituencies were young adults, independents and less-educated whites. A group that consistently gave him trouble, though, was self-identified Democrats. Whether that’s because the Clinton brand held a special allure for those voters or because they paid attention to the fact that Sanders had refused to join their ranks is unclear, but we may get a little clarity on it this time around. Brownstein:

Sanders, who has never formally identified with the Democratic Party, also consistently struggled among primary voters who consider themselves partisan Democrats, which is something of a hurdle for someone trying to win the Democratic nomination. Clinton won self-identified Democrats in every state with an exit poll except Vermont and New Hampshire, in Sanders’s backyard, and Wisconsin, where they tied. In the cumulative result, she beat him among Democrats by nearly two-to-one. Sanders’s weakness with Democrats partly reflected his troubles with African Americans, but Clinton posted a solid lead among white Democrats as well.

That argument is extra potent coming here from a black Democrat, Rep. Gregory Meeks, since black votes were the difference between victory and defeat for Clinton in the 2016 primaries. Meeks endorsed Hillary three years ago and is a Sanders critic of longstanding, having slammed him in 2016 for his “very troubling” record on gun control and then accused him of trying to “exploit black people” by criticizing Clinton for the 1994 crime bill that Bill Clinton signed into law. He hasn’t endorsed anyone in the 2020 race as far as I’m aware but what you’re seeing here is a sneak preview of the argument that will eventually erupt between Sanders and Kamala Harris. Bernie will try to ingratiate himself to black voters by attacking Harris’s record as a prosecutor; Harris will likely respond with some of the same criticisms Meeks made in 2016 as well as by zeroing in on Bernie’s persistent refusal to identify as a member of their party, as Meeks does here. That’s as close as his rivals will want to come to saying aloud that “democratic socialists” aren’t really part of the Democratic Party. By focusing on the narrow tribalist point about Bernie’s registration status, they can suggest to Democratic partisans that he’s not One of Us without declaring Bernie’s fans personae non grata as well. It’s a proxy for the battle over the party’s ideological identity.