[6] Polling of the potential match-up showed Markey trailing Kennedy by as much as 14 points, leading to speculation that he would retire rather than face a humiliating primary defeat, but he resolved to run for re-election.

[7] Kennedy faced skepticism about his reasons for running to replace Markey, and journalists observed that his campaign had difficulty articulating a clear rationale.

[8] Eventually, Kennedy's campaign pitch largely focused around a message that he would "show up" for disadvantaged residents of Massachusetts, something he claimed Markey had not been doing.

[9] This strategy was heavily inspired by Ayanna Pressley's successful campaign for the U.S. House the previous cycle, and was aimed at casting Kennedy as an insurgent outsider running against the establishment.

[9] Facing a severe polling deficit, Markey undertook to politically reinvent himself; his relatively low profile in Massachusetts gave him the opportunity to essentially define himself for the first time to many voters.

He was also endorsed by key figures in the party's progressive wing, such as Ocasio-Cortez, fellow Massachusetts Senator Elizabeth Warren, and the youth-led Sunrise Movement.

[19] As the race entered its final days the contest began to assume an ideological meaning, with New York writer Gabriel Debendetti writing that the contest was viewed as a "fight for the soul of the national Democratic party", with both candidates claiming that a victory for them would be an affirmation of the strength of the left-wing of the Democrats.