It sure looks like Joe Kennedy III will take the up-or-out path of challenging Senator Ed Markey in a high-profile, blockbuster 2020 primary. Democratic insiders are anticipating an announcement either at or soon after next weekend’s Democratic state convention in Springfield.

If true, it means a wide-open vacancy in the 4th congressional district, which Kennedy has represented since Barney Frank retired in 2012. The politically active region includes Newton and Brookline at its northern end, and Taunton and Fall River to the south.

Republicans will probably field a solid candidate — Norfolk state representative Shawn Dooley is the leading early name — but this should be an easy Democratic hold in a district likely to vote by a two-to-one margin against President Donald Trump.

It would be gauche, of course, for potential candidates to talk publicly about their interest before Kennedy actually makes his decision known. But, they want their names in the mix as party insiders gossip at the convention.

So what we have is a whisper-level rumor mill, and a lengthening list ranging from pure speculation, to those just wanting to be talked about, to serious early-stage campaigns.

That includes many of those who considered running, or began the process, seven years ago. Once Kennedy jumped in, however, they all withdrew or faded into irrelevance.

At least so far, nobody sees a potential field-clearer like that on the horizon.

That doesn’t mean all, or even many, of the names making the rounds will actually run.

More likely, the race — assuming it happens — will shape up similarly to the one that played out further north in the state last year, after Niki Tsongas announced her intention to retire from Congress.

Many known political figures considered running, and a few of them did.

But then, the field swelled with a variety of first-time candidates, many bringing a welcome and valuable perspective to the trail.

Running is one thing; mobilizing and leading a competitive campaign across a diverse congressional district is another. Still, bear in mind that some of the most intriguing candidates might be unknown to the usual political circles at this point.

Opening Roster
That said, here is an initial roster of names on the lips of Democrats in the 4th district’s political circles.

Back from 2012: Some serious political talent started to wade into the primary waters after Frank announced his retirement — only to drop back one by one from the weight of the Kennedy clout. Perhaps the biggest of those talents, Deb Goldberg, is now treasurer of the Commonwealth; she is said to be giving a hard look at the race, but the timing might not be right. Those who know well-connected Brookliner Jesse Mermell, now president of the Alliance for Business Leadership, say she sounds likely to jump in. There are mixed messages about Be The Change CEO and one-time U.S. Senate candidate Alan Khazei, with some saying he’s ready to go for it and others saying he hasn’t decided. Former District Attorney and Fall River mayor Sam Sutter’s name has been floated, but it’s unclear how seriously. Same with former Boston city councilor Mike Ross. Veteran state lawmakers Ruth Balser, Cynthia Creem and Marc Pacheco are probably happy just to be mentioned.

From the statehouse: State legislators have not fared well recently in seeking federal or statewide office, and they would have to forego a chance at re-election to shoot for the congressional seat. Most likely to risk it is state senator Paul Feeney of Foxborough, who has strong ties with Bernie Sanders liberals, trade unions and establishment Democrats. Rebecca Rausch of Needham might try to ride the momentum from her surprising state senate victory last November. New Brookline state representative Tommy Vitolo has the ambition, if he decides the time is right. Claire Cronin of Easton could be hampered by most of her state representative district lying outside the 4th congressional lines.

Municipal movers: Some likely local stepping-stone offices seem unlikely to produce a candidate. Fall River’s mayor, Jasiel Correia, is facing federal charges, including new allegations of extorting marijuana companies; Taunton mayor Tom Hoye is stepping down for an appointment as register of probate. But Paul Heroux, mayor of Attleboro, could take a shot. Newton city councilor Becky Grossman probably will, judging by the number of people who report getting calls from her father-in-law, former state treasurer Steve Grossman. That might box out another interested Newton city councilor, Jake Auchincloss. You might recall rock star congresswoman Alexandria Ocasio-Cortez coming to Brookline a few months ago to endorse a candidate for selectman; the recipient of that attention, Raul Fernandez, has eyes on this race.

Return to action: They are out or on their way out of elected office, but still harboring political dreams. Former New Bedford mayor Scott Lang has been itching to run for higher office and might get in this race despite his home city being carved out of the district several years ago. Outgoing Boston city councilor Josh Zakim — who succeeded Ross in his Back Bay district — has been having conversations about it. So has former Newton mayor Setti Warren. 2018 gubernatorial nominee Jay Gonzalez, of Needham, has been mentioned as a possibility.

Rookie runs: First-time candidates for elected office Lori Trahan and Seth Moulton showed it can be done. Brookline attorney Shannon Liss-Riordan took a bold leap into the U.S. Senate primary earlier this year; Kennedy’s entry will likely prompt her to leave that race in favor of seeking to succeed him. Brookline native Chris Dempsey, director of Transportation for Massachusetts and noted Boston Olympics naysayer, will consider running. David Simas, a Taunton native who became a high-level Barack Obama aide, would have to leave his gig as CEO of the Obama Foundation without seeing through construction of the Presidential Library in Chicago. And there are countless others in the region who might, even now, be mulling their first foray into the political arena. Stay tuned.