National Democrats are jumping into a hotly contested House primary in California, trying to avoid the disastrous situation of being left without a candidate in the general election in a Democratic-leaning district.

The Democratic Congressional Campaign Committee (DCCC) has launched ads against a pair of Republicans running for retiring Rep. Ed Royce’s (R-CA) district, hammering local Republican lawmaker Shawn Nelson’s “hypocrisy” for taking a government pension after promising not to and slamming former California state Sen. Bob Huff (R) for backing “billions in higher sales taxes.” The organization is spending $300,000 on cable, radio and digital ads.

The goal: To knock them both down so that only one Republican emerges in the race and Democrats don’t get locked out in a crucial pickup opportunity in their battle for House control.

California’s unusual all-party “jungle primary” means the top two candidates in the June primary election advance to the general election, regardless of party. In the past, that’s allowed two Republicans to advance in two competitive districts while a crowded Democratic field divides voters between several candidates — something Democrats are seriously concerned may happen again.

In this district, which Hillary Clinton won by nine points, there are just three competitive Republican candidates and five competitive Democrats. That means if Democrats split up their votes relatively evenly and no front-runner emerges over the next month, they’re at real risk of two Republicans advancing and their party blowing a winnable race.

The DCCC notably doesn’t go after GOP front-runner Young Kim, a former Royce staffer, in their attacks.

This district is one of four where Democrats are seriously worried they might not get a candidate through because of the high number of viable candidates running on their side — they’re also worried about getting candidates through against scandal-plagued Reps. Dana Rohrabacher (R-CA) and Duncan Hunter (R-CA), as well as the race for retiring Rep. Darrel Issa’s (R-CA) seat.

But national Democrats are facing a tough situation in trying to massage these races, as many past attempts to push out candidates or elevate one of their own over other Democrats have led to bitter responses from those candidates and a backlash against the party.

A move like this isn’t going to cause any problems for the DCCC, but it remains to be seen how well they manage these tensions going forward — especially if they feel they have to turn on one of their own in the race’s closing days to preserve their chance at a seat. Their early efforts to play in primaries haven’t always gone so well this year.