On Tuesday, Sen. Ed Markey and Rep. Joe Kennedy III will meet for the first time on the debate stage.

The match-up to determine who will be the Democratic candidate for the Senate — which pits incumbent Markey against a congressman with deep familial roots in politics — has captured the attention of the national press. In a presidential election year with many competitive congressional races, the Democratic party is also closely watching to see what the results of this primary signify for the 2020 election cycle. The debate, hosted by WGBH News, is one of the candidates' first major opportunities to show voters what sets them apart.

The race between the two narrowed after labor attorney Shannon Liss-Riordan dropped out of the race in January, saying "sometimes some obstacles are too great to overcome." Liss-Riordan built her campaign around her successful lawsuits on the behalf of workers against corporate and education giants like Starbucks, FedEx and Harvard University. Liss-Riordan made national headlines when she led a class action lawsuit on behalf of drivers against Uber, which eventually settled the case for $20 million.

Though Liss-Riordan entered with much of the same platform as Markey, she sought to make the case that she was an outsider with intimate knowledge of the struggles of the working class who could bring their perspective to the Senate. Her quest to unseat an entrenched Washington lawmaker was derailed when Rep. Joe Kennedy III announced in September that he was entering the race. New Bedford-raised businessman Steve Pemberton had also launched a bid for the seat, but was only able to stay in the race for about three months.

In his launch video, Kennedy presented himself as the person to bring Massachusetts into a new era of politics. In what has been widely seen as a direct critique of Markey, Kennedy called for “new politics” and for leadership “who [isn’t] afraid to break down an old system and build something better.” Even before he officially launched, momentum was building around Kennedy’s campaign. In a Sept. 7 poll from The Boston Globe and Suffolk University, Kennedy led the entire field. Worse for Markey, in a head-to-head match-up, he beat the senator by 14 points.

Building on his support from environmentalists, which include progressive champion New York Rep. Alexandria Ocasio-Cortez, 350 Mass Action and the youth-oriented Sunrise Movement, Markey challenged his opponents to a climate-focused debate minutes after Kennedy declared his candidacy. But Kennedy declined to appear.

Early in the race, Kennedy called on his opponents to sign a “People’s Pledge,” which would limit the amount of spending from outside groups in the Senate race. The move was widely seen targeting Markey, given that only days earlier, the group Environment Massachusetts announced its intention to spend $5 million in an independent expenditure campaign to support him.

With two candidates remaining, the Massachusetts political scene could be in for the beginning of a turbulent primary as Markey and Kennedy get ready to square off. Going into Tuesday's debate, Markey is carrying the support of 116 of the 200 lawmakers in the state legislature. The Democratic Senatorial Campaign Committee, the campaign arm of the Democrats in the Senate, has also backed him, along with Sen. Elizabeth Warren, who endorsed Markey prior to Kennedy’s entrance into the race. Kennedy, however, recently racked up the endorsements of 16 members of the U.S. House, including civil rights icon Rep. John Lewis, Rep. Joaquin Castro and Rep. Conor Lamb.

Though the two agree on most major issues, on Tuesday, Kennedy is expected to make the case that the solutions to a new era of problems require fresh faces in Congress. Markey, however, will likely tout his endorsements and his work in both the House and the Senate as to why he deserves another six years in office.