At Boston's preliminary mayoral election this week, voters put At-Large City Councilors Michelle Wu and Annissa Essaibi George on the ballot in November. Even though three of the five candidates were Black, none of them advanced to the November election. It's left many people wondering why.

GBH News editor Ken Cooper wrote an article for a journal at UMass Boston nine years ago, outlining the 13 factors, positive and negative, that lead to cities electing or not electing Black mayors. He joined GBH’s All Things Considered host Arun Rath to talk about how those factors played out in Boston's preliminary election.

Arun Rath: Why do you think that none of the three Black candidates — Acting Mayor Kim Janey, City Councilor Andrea Campbell and former economic development chief John Barros — why none of them were able to assemble a winning coalition?

Ken Cooper: Well, the research I did indicates the likeliest way that a city elects a Black mayor is with a coalition of Black voters and white progressives. There's a lot of thought that perhaps the better coalition is, sort of, a coalition of people of color, sort of a rainbow coalition, perhaps a Black-brown coalition. But the research shows that allying with white progressives is more likely to succeed.

And the reason for that is that each ethnic group sort of is more committed to their own and excited about voting for their own than voting for others. So, in the case of the three candidates — the three Black candidates — in the mayoral election, it's pretty obvious neither of them were able to win over enough white progressives and it's pretty obvious the reason was because Michelle Wu, who's of Chinese descent had, won the favor of progressives and captured their imagination.

Rath: My first thought was that, were there too many black candidates running, in terms of splitting the vote? Of both of black voters and white progressives that you're talking about?

Cooper: This is where I sort of depart from conventional wisdom. The idea that you have to have a single Black candidate to elect a Black mayor sort of is premised on the idea that voting will be racially polarized, that white voters won't vote for a Black candidate.

I think it depends. I mean, in this particular circumstance, you could have had two finalists and both were Black, if they were able to assemble a wider and broader coalition. So I'm not one who subscribes to, "The only way that you can win, elect a Black mayor, is by having a single Black candidate." In fact, my article talks about the experience of my hometown, which happens to be Denver, Colorado, where the first time they elected a Black mayor, it did so because both finalists for Black. One was the elected city auditor, the other was the elected district attorney. So, it's not necessarily so you have to unify a Black community behind a single Black candidate to capture the mayoral office.

Rath: Well, I'm very curious to ask you, because you've looked at all the factors going into this: in terms of electing a Black mayor in Boston — or anywhere else, but looking at Boston — is it as simple as the size of the Black population? Are there not enough Black people in Boston to make sure a Black mayor gets elected? Somehow I think it's not that simple.

Cooper: It is not that simple. It's often been said — and maybe not this cycle, but before this, I heard it many times — that, "Oh, the Black population is too small to elect a Black mayor in Boston." And I would point out that my hometown — again, Denver — the population is smaller, the Black population, and the same is true in Seattle, and Kansas City and all those places have had Black mayors.

Population size does play a role in Boston, but not in that way. Turns out that a middling minority of 20 to 35% — and Boston falls within that range — has the hardest time electing a Black mayor. Obviously, if you have a Black majority, a city, it's easier, but it's often easier for a city at like 10, 12% like Denver.

And I think the reason is, and scholars don't speculate on this, is that when the population is that small, it's not a threat — or a perceived threat — that Black people are taking over if you have a black mayor, because obviously white people have voters have elected that mayor and he has to sort of serve their interest to a large degree if he wants to get elected again. Population size is a factor, but it's not as simple as being too small to do it.

Rath: You talked about the difficulties of the Black electorate as being monolithic, having them rally behind whoever the Black candidate is. There was this effort led by former State Senator Dianne Wilkerson — this effort was called Wakanda II — which attempted to unite Black voters behind a single candidate, that was Acting Mayor Kim Janey. How difficult is that to do?

Cooper: Well, in Boston, it's quite difficult. And people who know Boston's Black community well understand this. It's a diverse community, internally diverse. You have people born in Boston, you have people born outside of Boston but in the United States, you have people with roots in the Caribbean or the Cape Verde Islands and all those groups don't cohere very well.

One of the factors scholars cited was, you know, internal cohesion of a community, and it's one thing. In fact, Boston's Black community has a lot of internal divisions. The idea that you would have an organization, presumably neutral, that would vet candidates for office and endorse the one the most likely to act mostly in the interest of a Black community, it's a good idea. I think the problem with Wakanda II, it sprang up specifically for this particular election, and it makes me wonder how much credibility, authority they would have — and how much trust voters would have in their word — if it hadn't been a standing organization that had been around for some years.

Rath: So, with all these factors in consideration — and it's a lot to do for me to hold in my head — but looking looking forward and into into Boston's future, how likely do you think it is, considering these factors, that Boston will — or how long do you think it would take? What would you think it would take for Boston to to elect a Black mayor?

Cooper: I'm not going to make any predictions about how long, because someone I know once quoted me that we'd never have a Black president in my lifetime, which turned out not to be correct, obviously. I would say that I think what is needed to elect a Black mayor of Boston — whenever it happens — is, there needs to be greater political organization within the community, greater cohesion — that doesn't mean unanimity — but cohesion and greater mobilization of Black voters.

These two out of the three Black candidates who didn't make the final round, there were enough votes un-cast in the Black community to propel either or both of them into the final two. And those votes weren't cast, and that's one reason their campaigns over.

Rath: Ken, this has been fascinating. You're a great editor, it's just a treat for people to get a sense of the depth of knowledge that you have — that we get access to. Thank you for this.

Cooper: Thank you, Arun.

Rath: That's GBH's Ken Cooper. This is GBH's All Things Considered.