BOSTON — The scramble to succeed outgoing U.S. Rep. Niki Tsongas is shaping up to be the marque race on the 2018 ballot, with at least a dozen declared candidates running for the open seat.

But it also features one of the most ethnically diverse group of individuals ever to run for Congress in Massachusetts, political observers say, with candidates whose roots span the globe from Asia to the Middle East to the West Indies.

Dan Koh, an Andover Democrat, was one of the first contenders to join the race and has been stressing his family's story of emigrating to the Merrimack Valley from Korea and a section of Syria that is now Lebanon, as he builds name recognition across the district ahead of next year's Democratic primary.

Koh said the diversity of the congressional race reflects the state and region's changing political landscape.

"It's sign of how open this district is to people of all different cultures and ethnic backgrounds," he said. "The times are clearly changing."

Rep. Juana Matias, a Lawrence Democrat, is a first-generation immigrant from the Dominican Republic who is making her inaugural run for Congress in the district that stretches along the New Hampshire border from Winchendon Springs to Haverhill and south to Marlborough.

"Diversity is our country's greatest strength and it's important to ensure that our government is representative of other demographics," she said.

Matias, one of the first Latinas elected to the state Legislature, said she is running "on behalf of all working people."

"I know what it's like to live paycheck to paycheck," she said. "I grew up in a blue-collar family with both my parents working in factories most of their lives."

Democrat Nadeem Mazen, the state’s highest-profile Muslim elected official, is also running for the seat. He's a Cambridge City Councilman who grew up in Andover where his Egypt-born father and mother from Indiana settled about 30 years ago.

He says he'd be proud to become the state's first Muslim congressman, but doesn't want to be pigeonholed as "the Muslim candidate."

"We're in a time when too many people cherish identity politics," he said. "I'm focused on the work for the overall community, on American's economic primacy, education leadership and health care options."

That said, Mazen said he wouldn't hesitate to stand up against bigotry and discrimination targeting people of his faith or ethnicity.

"The same way black, Latino, Jewish and working-class leaders have done since the inception of this country," he said.

Democrat Abhijit "Beej" Das, president and chief executive officer of Troca Hotels, could also break ground as the state's first Indian congressman.

And Steve Kerrigan, a Lancaster Democrat who jumped into the race two weeks ago, would be the state's first openly gay congressman since Democrat Barney Frank stepped down in 2013.

Besides Matias, several other women are also seeking to succeed Tsongas, who in 2007 became the first Massachusetts woman elected to Congress in 25 years.

State Sen. Barbara L'Italien, an Andover Democrat, and Lori Trahan, a Westford Democrat, both want to keep the district in a woman's hands.

Aside from Tsongas and Sen. Elizabeth Warren, the only other woman in the 11-member delegation is Rep. Katherine Clark.

Woman outnumber men among the state's 6.8 million residents, but only 26 percent of state lawmakers are female, according to Linnea Walsh, interim executive director of the Massachusetts Woman's Political Caucus, a nonpartisan group that works to elect women.

Her group, which hasn't yet endorsed a candidate, doesn't want to see the 3rd Congressional District to flip back to a man.

"There's a big gender gap when it comes to fair representation," she said. "We're going to looking at the 3rd Congressional and other races across the state to see how we can work towards greater parity."

Erin O'Brien, chairwoman of the political science department at the University of Massachusetts at Boston, said minorities are generally underrepresented in the state's political classes. The state's congressional delegation is all white and made up almost entirely of men.

"Massachusetts traditionally elects white men," she said. "We're really poor at electing people of color and women, particularly women of color."

Still, she notes, the state has a track record of breaking barriers, citing the election of Democrat Deval Patrick in 2006 as the state's first black governor.

Some suggest the current crop of 3rd District contenders is motivated, in part, by opposition to Republican President Donald Trump, whose policies targeting immigrants, Muslims, women and ethnic minorities have infuriated activists and alienated many independent voters in the state.

Both Matias and Mazen have described themselves as "Donald Trump's worst nightmare" in recent interviews.

"I am who I am today because of American values," Matias said. "And many of those American values are under threat from the Trump administration."

Michael Goldman, a Democratic strategist, points out that many of those running represent constituencies marginalized by the Trump presidency.

"They want to go to Washington to fight the good fight," he said. "But ultimately the field is going to narrow as the primary gets closer."

Christian M. Wade covers the Massachusetts Statehouse for North of Boston Media Group’s newspapers and websites. Email him at