Democratic officials added eight candidates on Monday to a list of top contenders in congressional midterm battlegrounds, wading into a handful of contested primaries to make clear the party leadership’s preference in some of the country’s most critical districts.

The additions by the Democratic Congressional Campaign Committee to its “Red to Blue” program bring the number of candidates on the list to 20. The initiative primarily focuses on seats that party leaders believe they can flip. The designation typically offers candidates a significant fund-raising lift from donors.

In at least half of the races where the party is elevating a candidate, there is a seriously contested primary. One of those contests is in California’s 22nd Congressional District, around Bakersfield, where Representative David G. Valadao, a Republican, has survived past attempts to oust him.

The D.C.C.C. is elevating Jasmeet Bains, a doctor and California assemblywoman, over Randy Villegas, who has the endorsement of the Congressional Progressive Caucus and the Congressional Hispanic Caucus’s campaign arm. In California, all candidates run in the same primary, and the top two advance to the general election, regardless of party.

The party is also wading into Pennsylvania’s Seventh District in favor of Bob Brooks, who is president of a firefighters union. He has the unusual endorsement combination of the Blue Dog PAC, a moderate faction; Senator Bernie Sanders of Vermont, a leading progressive; and Gov. Josh Shapiro of Pennsylvania. Mr. Brooks faces a primary against Ryan Crosswell, a Marine veteran and Justice Department official, who out-raised Mr. Brooks last quarter.

Republicans are defending a narrow House majority in the midterms in the face of headwinds including President Trump’s low approval rating, high gas prices and an unpopular war in Iran.

Democrats are feeling emboldened after a series of strong performances in special elections. Still, the party’s internal divisions, playing out in primaries across the country, remain a major challenge. As the American political battleground has shrunk in recent decades, winnowed by polarization and gerrymandering, the remaining competitive corners of the country have received outsize attention.

The D.C.C.C. has identified 44 Republican-held or open House districts that it believes are in play. It says that the “Red to Blue” program will support Democratic candidates in most of those districts by Election Day.

“House Democrats have the momentum to take back the majority,” Representative Suzan DelBene of Washington, chair of the campaign committee, said in a statement.

The National Republican Congressional Committee has a similar program for top recruits: the “MAGA Majority.” It has 17 candidates for 2026 as of last week.