Sen. Ed Markey won the Massachusetts Democratic primary for the U.S. Senate on Tuesday evening,fending off a bitter challenge from Rep. Joe Kennedy, AP reports.

Why it matters: The power of the Kennedy name in Massachusetts wasn't enough to overcome the incumbency advantage and progressive credentials of Markey, the co-author of the Green New Deal.

Background: The race captured a unique generational dynamic between the Democratic Party's progressive and establishment wings.

• 74-year-old Markey was backed by progressive champions like Rep. Alexandria Ocasio-Cortez (D-N.Y.) and Sen. Elizabeth Warren (D-Mass.), while the 39-year-old Kennedy earned endorsements from party leaders like House Speaker Nancy Pelosi.
• Pelosi served with Markey in the House for 25 years, before he was elected to the Senate in 2013 during a special election to replace former Sen. John Kerry, who had been nominated as Secretary of State.
• Kennedy, the grandson of former Attorney General Bobby Kennedy and grand-nephew of former President John F. Kennedy, was elected to the House in 2012. He is the first Kennedy to lose a statewide race in Massachusetts.

The big picture: Even though Markey is an incumbent, his win is considered a big one for the progressive movement, which has seen mixed results this election cycle.

• Progressive Jamaal Bowman defeated 16-term incumbent Rep. Eliot Engel in NY-16's Democratic primary in June.
• Establishment favorite Amy McGrath defeated progressive state Rep. Charles Booker in Kentucky's Democratic U.S. Senate primary the same month.