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 later this year. Biden, who served in the Senate for 36 years, has led the primary field in congressional endorsements so far.

Lamb's 17th District includes a portion of Cranberry Township, all of Beaver County and the North Hills, part of the South Hills, and Allegheny Valley in Allegheny County.

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 in 2018. 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.”

Lamb and Houlahan both noted Biden's potential strength in Pennsylvania, which is expected to be a top presidential and House battleground this year. Had the new congressional map been in place in 2016, Trump would have carried Lamb's 17th District in the Pittsburgh suburbs by 2 percentage points while Hillary Clinton would have won Houlahan's 6th District in the Philadelphia suburbs by 10 points. Inside Elections with Nathan L. Gonzales rates Lamb's race Likely Democratic and Houlahan's race Solidly Democratic.

Trump carried the Keystone State by less than 1 point in 2018. The state's only Democratic senator, Bob Casey, has endorsed Biden, who has roots in Scranton.

“Pennsylvania is not red or blue but a purple place which our next president needs to carry to win,” Houlahan said in a statement. “Joe Biden can win Pennsylvania, and I'm proud to endorse him.”

Luria also noted that Biden could win a competitive House district like hers in Virginia, which Trump carried by 3 points in 2016. Luria could be facing a competitive election in 2020.

“Joe Biden is 'battle-tested' on the world stage, in Congress, and in the White House. He will defeat Donald Trump and win in tough districts like mine,” Luria said in a statement.

Conor Lamb