David J. Trone, seen in March 2016, announced he will run for the congressional seat being vacated by Rep. John Delaney (D-Md.). (Marlon Correa/El Tiempo Latino)

Rep. John Delaney’s decision to forgo reelection next year has triggered a burst of interest in what is arguably Maryland’s only congressional swing district.

On Wednesday, wine magnate David J. Trone and state Sen. Roger Manno announced that they would compete in June’s Democratic 6th District primary, joining state House Majority Leader Bill Frick, Del. Aruna Miller and retired intelligence officer Andrew Duck — who twice ran for the seat years ago, when it was firmly in Republican hands.

Republicans could have a race on their hands, as well. Matt Mossburg, a former delegate, is running, and Amie Hoeber, Delaney’s 2016 challenger, is considering it.

The filing deadline is in February.

Delaney, who announced Friday that he would seek the Democratic presidential nomination in 2020, has represented the 6th District since 2012, when he ousted longtime incumbent Roscoe G. Bartlett (R) after a partisan redistricting effort that is now under court challenge.

Rep. John Delaney’s decision not to run again has sparked a crowded Democratic primary. (Jacquelyn Martin/AP)

The Democrat barely defeated Republican Dan Bongino in 2014, when Gov. Larry Hogan’s surprise victory boosted GOP turnout. But Delaney easily triumphed over Hoeber in November, even though she had support from the national party.

The redrawn district stretches from Montgomery County through Western Maryland. Of the candidates running so far, only Duck, Miller and Mossburg live in the 6th District, which candidates are not required to do. The others live in the neighboring 8th District, as does Delaney. Only Manno would commit to moving to the 6th District if elected.

Trone, who lives in Potomac, spent more than $13 million of his own money running for a different seat in Congress last year, losing to then-state Sen. Jamie B. Raskin in the 8th District primary, one of the most expensive House nominating contests ever.

He is expected to open his checkbook again this time and has vowed to reject campaign contributions from corporations, lobbyists or political action committees. In a video launching his campaign, Trone said he would “pick up right where John leaves off.”

“I’ll fight President Trump and Congress’s attempts to gut health care, women’s rights, education, the environment and Social Security,” he says. The video describes Trone’s experience growing up on a family farm that eventually went bankrupt, and he said that if elected, he will seek funding for the National Institutes of Health, based in Bethesda, and transportation projects.

Delaney stopped short of endorsing Trone but issued a statement Wednesday praising his “deep commitment to both public service and to bringing his business experience to the political debate.”

Hours after Trone’s announcement, Manno made his campaign official, touting his experience working as a Capitol Hill policy staffer when the Affordable Care Act passed.

Manno, who lives in Silver Spring and who has served in the legislature since 2007, said he will focus on health care and economic issues in the race.

Frick, of Bethesda, rose to leadership in the state House of Delegates over three terms and said he’s most proud of legislation to increase the state’s reliance on clean energy — which survived a Hogan veto — and to create a mechanism for workplace retirement savings accounts.

Miller, an engineer who lives in Darnestown, was first elected to the legislature in 2010. She has pushed for bills requiring electronic monitoring of domestic violence perpetrators and extending the statute of limitations for sexual offenses against minors.

She is the only woman so far in the race to join a congressional delegation that has been all-male since the retirement of longtime senator Barbara A. Mikulski and the departure of congresswoman Donna F. Edwards last year. There are currently seven Democrats and one Republican member.

Duck, who works at the Pentagon as a contractor and lives in Frederick, Md., challenged Bartlett in 2006, 2008 and 2010 and says his campaigns registered enough Democrats to show those voters’ strength as a voting bloc before the district lines were redrawn.

On the Republican side, Mossburg, also of Frederick, served one term as a state delegate in the late 1990s. He said his personal recovery from opioid addiction and advocacy work qualify him to tackle the problem, which is particularly acute in Western Maryland.

Hoeber, who lives in Potomac, is a defense expert who restarted her international affairs consulting business after losing to Delaney last year.