Three House Democrats who flipped Republican-held districts in 2018 announced Sunday that they are endorsing former Vice President Joe Biden in the crowded presidential primary. All three served in the military.

Pennsylvania’s Conor Lamb, a Marine veteran, and Chrissy Houlahan, an Air Force veteran, along with Elaine Luria of Virginia, who is a retired Navy commander, all said Biden is the right candidate to unify the country. Last week, first-term Iowa Democratic Rep. Abby Finkenauer also announced that she was backing Biden.

Their endorsements come as Biden has argued his candidacy would boost Democrats in competitive House and Senate races in 2020. Biden, who served in the Senate for 36 years, has led the primary field in congressional endorsements so far.

Biden endorsed all three Democrats in their 2018 races. Lamb referenced Biden campaigning for him in 2018, when Lamb pulled off an upset by winning a special election in a House district Trump carried by 20 points. Lamb later won a full term in a new district due to a redrawn congressional map.

“When he came to campaign for me … I saw huge crowds of working people cheer for him. I watched him stop and thank each police officer he passed. I heard him greet our local union leaders by name,” Lamb said in a statement from the Biden campaign. “Joe Biden respects our people, he knows what they are going through, and he knows what it means to keep your word.”