Sen. Ed Markey faces off Tuesday against challenger Rep. Joe Kennedy III in a Massachusetts Democratic Senate primary. Markey is considered a heavy favorite in the race.

Markey, 74, served for 37 years in the House before he was elected to the Senate in 2013 to replace John Kerry. Markey, a progressive, helped author the Green New Deal legislation with Rep. Alexandria Ocasio-Cortez, D-N.Y., and supports Medicare for all.

Kennedy, 39, has represented Massachusetts 4th congressional district since 2013 and is a grandson of former Senator and Attorney General Robert F. Kennedy, who was assassinated in 1968. In January 2018, Kennedy gave a response to a State of the Union address from President Donald Trump.

Kennedy announced his primary challenge against Markey in September and claims the incumbent has not done enough for Massachusetts. Kennedy has criticized Markey’s vote in favor of the Iraq War and the 1994 crime bill.

The race has divided top Democratic figures, with House Speaker Rep. Nancy Pelosi, D-Calif., endorsing Kennedy. The other Massachusetts senator, Elizabeth Warren, has endorsed Markey, along with Ocasio-Cortez, who has been featured in an ad for his campaign.

“When it comes to progressive leadership, it’s not your age that counts, it’s the age of your ideas, and Ed Markey is a leader we need,” Ocasio-Cortez said in the ad.

Although Kennedy was originally seen as likely to unseat Markey, the incumbent has managed to revamp his image. Markey’s progressive views, Nike sneakers, and online fan base have given his campaign some momentum, especially with young activists.

A WHDH/Emerson poll conducted in late August showed Markey leading Kennedy by 12 points, 56% to 44%. An Emerson survey in early May showed Kennedy ahead by 16 points, 58% to 42%.

If Kennedy loses on Tuesday, he will be first in the Kennedy Family dynasty to lose an election in Massachusetts.