Sen. Ed Markey (D) on Tuesday successfully fended off a challenge from Rep. Joe Kennedy III (D) in the Massachusetts Senate primary after facing what was initially seen as an uphill climb against a rising Democratic star and member of the most famous political family in the U.S.

Those close to Markey attribute his success to robust progressive support at the grassroots level as well as a slow and steady campaign strategy.

“Start with the better candidate, deliver a positive message and then organize like hell,” Markey’s campaign manager John Walsh told The Hill in an interview last week.

The senator himself addressed his supporters during his victory speech on Tuesday, calling his win a "reaffirmation" of the progressive movement.

"Tonight is more than just a celebration of a movement," Markey said, speaking from his hometown of Malden, Mass. "It is a real reaffirmation of the need to have a movement, a progressive movement of young people demanding radical change, demanding justice."

The incumbent senator's victory comes nearly a year after Kennedy, 39, entered the race with a double-digit lead over the 74-year-old incumbent senator, drawing media attention from Massachusetts and beyond.

A Change Research survey conducted in August 2019 before Kennedy announced his candidacy showed the congressman with a whopping 17-point lead over Markey.

But polls in recent weeks signaled the tables had turned, with Markey leading his opponent by double digits in some cases. Now, Kennedy has become the first member of his family to lose a statewide race in Massachusetts.