Baca has yet to announce any endorsements from his former colleagues. The endorsements are a signal to outside money and party activists to back Aguilar over Baca and attorney Eloise Reyes (D), whom the pro-abortion-rights EMILY's List has hinted it might endorse.
Miller won the seat over another Republican in the general election in 2012 after Aguilar and other Democrats split the Democratic vote in California's unusual all-party primary, where the top two vote-getters advance to the general election.
None finished in the top two spots, giving Miller a clear path to the general election win.
A divided Democratic party could make it more difficult to win the seat again in 2014, though no Republican other than Miller has yet emerged to run in the primary — meaning that at least one Democrat should be on the general election ballot.
Half of Aguilar's new endorsers include five freshmen who never served with Baca: California Democratic Reps. Julia Brownley, Alan Lowenthal, Scott Peters, Eric Swalwell and Mark Takano. The others: Reps. Henry Waxman (D-Calif.), Karen Bass (D-Calif.) Judy Chu (D-Calif.), Janice Hahn (D-Calif.) and Adam Schiff (D-Calif.).
Two earlier endorsers, Reps. Gloria Negrete McLeod (D-Calif.) and Loretta Sanchez (D-Calif.), have long had antagonistic relationships with Baca.
Aguilar has some strong local support as mayor of a major town in the district, but the outside endorsements may not give him that much of a boost.
In another southern California district last year, then-Rep. Howard Berman (D-Calif.) was backed by nearly the entire state delegation in his race against fellow Rep. Brad Sherman (D-Calif.). But Sherman easily won the race anyway.