A Republican super PAC is launching a last-minute effort to boost a handful of House GOP candidates in southern California. The goal is to block Democrats from getting a candidate into the general election in some key House races.

The American Future Fund, an Iowa-based GOP group, has dropped almost $700,000 to boost four GOP candidates in three districts, according to documents filed with the Federal Election Commission on Wednesday.

Their goals are to elevate some flagging Republicans and try to help them make the November ballot in districts that are key to Democrats’ hopes of winning the House this fall.

California’s “jungle” primary system allows the top two vote-getters to advance to the general election, regardless of party. That’s led to concerns among Democrats that their candidates could split the Democratic vote, allowing Republicans to finish in the top two spots in some congressional races and immediately costing them chances at a handful of winnable seats in the state.

National Democrats have been spending heavily to try to avoid that scenario.

Republicans had been surprisingly quiet in their response, considering how with some effort now they could guarantee victory in a few key House battles — as well as save themselves a lot of money in November in the expensive districts. But this buy suggests things may be starting to shift.

The GOP super-PAC’s buy includes almost $500,000 on advertising, direct mail and door-to-door voter outreach to boost Rocky Chavez and Diane Harkey, a pair of Republican candidates running for the seat currently held by Rep. Darrell Issa (R-CA), who is retiring. That race is one in which both parties worry they might get shut out and fail to get a candidate through to the November election, though Democrats are more alarmed at the prospect.

The group is also spending $100,000 to boost Scott Baugh, a Republican running against controversial Rep. Dana Rohrabacher (R-CA). That district is the one where Democratic concerns about being shut out, given their own crowded field, are most acute.

The GOP group is also chipping in about $100,000 to boost Young Kim, the GOP front-runner in the crowded race to replace retiring Rep. Ed Royce (R-CA).

The efforts for Kim and Harkey began last week, but this is the first evidence that the group’s push is to block Democrats out in some of these districts, rather than help out particular GOP candidates. The group didn’t respond to requests for an explanation of their strategy.

Republicans had expressed growing frustration that their party wasn’t doing more to meddle in these primaries to ensure the best results. Democrats already have spent millions on the races.

Issa told TPM on Tuesday, before these ads had become public, that House Minority Leader Nancy Pelosi’s Democrats were doing a better job organizing in the state, even in traditionally conservative enclaves like his district.

“Pelosi naturally gets us better. That’s not to say anything against Steve,” Issa said, referring to National Republican Congressional Committee Chairman Steve Stivers (R-OH). “It’s just that the observation in my district is the Democrats are playing a game that could well get one of their candidates in that otherwise wouldn’t if both sides were playing.”

Other Republicans have also griped about the lack of national intervention to help them.

“You wish the party would recognize this opportunity and lift us up,” GOP strategist John Thomas, who’s working with candidate Shawn Nelson in Royce’s district, told TPM. “They just don’t understand the top-two dynamic.”

Democrats have been spending heavily against Nelson and Bob Huff to avoid them getting into the runoff with Kim, the GOP front-runner, and Republicans still have done little in response to help them.

But the American Future Fund’s late intervention could help move the ball back in Republicans’ direction in these key seats.