Ayanna Pressley gives a late blessing to Michelle Wu

Her coveted endorsement is valuable. But the timing of the endorsement — after, not before, the preliminary election — inspired grumbles: When it came down to giving either one of two Black women in the race the boost they needed to win, Pressley stayed on the sidelines.

City Councilor at Large and candidate for mayor Michelle Wu and Representative Ayanna Pressley pose for a photo with supporters during a canvassing event in Hyde Park, Oct 2. Pressley endorsed Wu in the Boston mayoral race.Craig F. Walker/Globe Staff

Everyone running for mayor of Boston wanted an endorsement from Ayanna Pressley, who, just three years ago, was the first Black woman elected to Congress by Massachusetts voters. In the run-up to the final election, City Councilor Michelle Wu got it.

Now two things about that coveted endorsement are true. First, as endorsements go, it’s valuable. In Washington, Pressley’s progressive voice and membership in “the Squad” have given her a national profile. Back at home, she’s probably the most powerful elected official in Boston, given her unique connection to Black voters and white liberals, and the power vacuum created when Mayor Marty Walsh left to become US labor secretary. But the timing of Pressley’s endorsement — after, not before, the preliminary election — also inspired grumbles: When it came down to giving either one of two Black women in the race the boost needed to win, Pressley stayed on the sidelines.

Both Acting Mayor Kim Janey and City Councilor Andrea Campbell sought Pressley’s blessing, sources with each campaign told me. Neither got it and neither one made the final cut, which means the next mayor won’t be Black. (Pressley’s husband, Conan Harris, supported John Barros, the only Black man in the race, who finished last.) Those results were a big disappointment to Black voters who saw this election as a unique opportunity to usher in a new era in Boston politics. Instead, the city’s Black politicians are once again playing a backup role, with no immediate path to a starring role as mayor.

Janey was first to throw her support to Wu, a key development given Janey’s strong preliminary election showing in Boston’s Black neighborhoods. Then Pressley jumped in. Endorsements don’t guarantee votes. But in this case, they send a message of unity around Wu’s candidacy. Meanwhile, Wu’s opponent, Councilor Annissa Essaibi George, has been trying to put together the same coalition that helped elect Walsh. While she has support from unions and city workers, so far her campaign shows no overt signs of being able to expand her base into Boston’s Black and brown neighborhoods as Walsh did.

Essaibi George told the Globe she, too, asked Pressley for her endorsement, but the prize went to Wu, who shares Pressley’s appetite for progressive causes. In endorsing her, Pressley called Wu her “friend and sister in service” and praised her for having “a passion for service and a vision for our city that is grounded in her own lived experience and belief in the transformative potential of policy.”

Endorsements follow their own political machinations. Senator Edward J. Markey just endorsed Wu, even though Essaibi George endorsed Markey at a time when the political world was certain he would lose a primary challenge from then-US Representative Joe Kennedy. However, with help from some of the same young progressive activists who now support Wu, Markey won that battle. A year later, he apparently felt he owed progressives something more than he owed Essaibi George.

Pressley was faced with a difficult choice between two Black women; staying out of the preliminary was unquestionably easier than getting involved. If Janey or Campbell had gone on to win the mayor’s office, either would have established their own power base. Of course, power will shift back to the new mayor, no matter who it is. If Wu becomes Boston’s first Asian American mayor, she will attract her own national headlines. And if she wins, Pressley’s endorsement will also be seen as significant.

Three weeks out from election day, it feels like fall, and it feels like Wu has the momentum. But as everyone knows, wait a minute and New England weather changes. Wu is winning the endorsement battle to the extent that she now looks like the candidate of the establishment, not a mayor who will take it on. At some point, do these endorsements backfire, giving Essaibi George more appeal as an insurgent? It’s possible, but not likely.

With Pressley’s endorsement, the key question is whether it increases Black voter turnout for Wu. If it does, Pressley takes credit as queen-maker in a city that is not used to having one, for a mayor who will make history in her own way. But that mayor won’t be Black.