California is ground zero for Democratic efforts to regain the House in 2018 but the state’s unusual primary system may derail Nancy Pelosi’s hopes of becoming speaker again.

There are seven Republican-held districts in the state that Hillary Clinton won in the 2016 presidential election. However, it’s possible that several of them will not have a Democrat in the ballot in November.

The state’s 5 June primaries feature an unconventional “top two” primary that could lead to a host of unintended results. Passed by a ballot initiative in 2010 in an attempt to encourage more moderate elected officials, the “top two” replaced traditional party primaries with a free for all where candidates from every party would compete in an open primary. The top two candidates would advance to the general election in November regardless of party affiliation. It hasn’t worked that way at all.

As Brian Brokaw, a top Democratic strategist in the state, told the Guardian, it’s had the opposite the effect. “It’s mirrored the closed primary situation. The way for a Democrat to advance or a Republican to advance is play to the base.” Further, voters have still yet to grow used to the unusual system. Sal Russo, a California based conservative operative, pointed out “it kind of leaves everyone a little confused and there just doesn’t seem to be the energy since they brought this system”.

Since California implemented the system, two competitive House races have been left with only candidates from the same party running in the general election. Each time it has happened, the two candidates have been Republican. However, in a year when Democrats are running for office in unprecedented numbers, the risk now looms in three key districts.

Democrats are most worried about the 48th district, which is represented by Dana Rohrabacher, a longtime Republican incumbent who has long been painted as “Putin’s favorite congressman”. A traditionally conservative district that contains wealthy coastal enclaves in Orange county, it was narrowly won by Hillary Clinton in 2016. The changing political dynamics and Rohrabacher’s unusual politics, which have led fellow Republicans to joke he was on Putin’s payroll, made the seat a target. Two well-to-do Democrats, scientist Hans Keirstead and businessman Harley Rouda, were vying for the chance to take Rohrbacher and Democrats felt relatively comfortable with either candidate in November.

Facebook Twitter Pinterest Democrats are most worried about the 48th district, which is represented by congressman Dana Rohrabacher, a longtime Republican incumbent. Photograph: Bill Clark/CQ-Roll Call,Inc.

However, all those calculations were changed drastically when another prominent Republican jumped in at the last minute. Scott Baugh was a former Republican leader in the state assembly and chairman of the Orange county Republican party. He positioned himself as an alternative for those Republicans who might not share Rohrabacher’s favorable views of controversial figures like Vladimir Putin and Julian Assange. In polling, Rohrabacher is currently holding steady in the low 30s according to one national Democratic strategist. The result is that there was room for Baugh to finish second and squeeze out a Democrat from appearing on the ballot in November.

Baugh’s emergence sparked a panic among Democrats. Several lagging candidates dropped out and the Democratic Congressional Campaign Committee, the campaign arm of House Democrats, actively endorsed Rouda in effort to consolidate the vote. Outside groups, like the House Majority PAC, the Super Pac tied to House Democrats, has spent over $650,000 in attacks against Baugh on television.

However, there are two other seats where Democrats are at risk of being shut out as well. In California’s 39th district, an open seat vacated by Republican Ed Royce, the chair of the House Foreign Affairs Committee has become the scene of a vicious Democratic civil war. Gil Cisneros, a veteran and lottery winner backed by national Democrats has faced a number of attacks from Andy Thorburn, a progressive businessman backed by a number of outside liberal groups. The back and forth became so heated that a formal truce had to be brokered between the two campaigns for fear that the bitterness would allow a second Republican to make the general election alongside Royce’s anointed successor, assemblywoman Young Kim. Such a result would be a disaster for Democrats in a majority minority seat that Hillary Clinton won by nearly nine points in 2016.

The other seat at risk is the San Diego area seat held by retiring congressman Darrell Issa. Issa won re-election by only 1,600 votes in 2016 while Hillary Clinton beat off Donald Trump by a margin of 7.5%. However, a crowded Democratic primary for the seat has scrambled things with three strong candidates, Doug Applegate, the Democratic nominee in 2016, Mike Levin, an environmental lawyer and Sara Jacobs, the 29-year-old granddaughter of the founder of telecommunications giant Qualcomm. With one Republican, Diane Harkey, likely to make the general election, national Democratic groups have run ads against Rocky Chavez, a Republican assemblyman, to make sure that at least one Democrat is on the ballot in November.

Facebook Twitter Pinterest The other seat at risk is the San Diego area seat held by retiring Republican congressman Darrell Issa. Photograph: Olamikan Gbemiga/AP

Yet for all the money spent and all the anxiety, not all Democrats are worried. Paul Mitchell, who runs the California-based data firm Political Data Inc said “a lot is being made of a low likelihood event”. Instead, Mitchell compared it to an earthquake – “if it does happen, it could be very catastrophic” – but dismissed the risk in any given district as no higher than 10 or 15%.

For all the struggles that Democrats have had with the top two primary though, Republicans have not been left unscathed either. The state’s deep blue lean has meant that it is a virtual certainty that the Senate race on the ballot in November will feature two Democrats, longtime incumbent Dianne Feinstein and Kevin de Leon, the outgoing state senate president pro tempore. De Leon is challenging Feinstein from the left as a progressive.

But Republicans had been worried that a similar situation may pop up in the governor’s race. The democratic lieutenant governor, Gavin Newsom, has long been considered a shoo-in to make the November ballot. However, there was anxiety among Republicans that the former Los Angeles mayor, Antonio Villaraigosa, might finish in the second spot and leave the GOP shut out from the two top of the ticket races in November. In recent days though, Trump has tweeted several times in support of the leading Republican candidate John Cox. In addition, Newsom has attacked Cox as well in hopes giving him publicity. Cox, a businessman who mounted a quixotic bid for the presidency in 2008, is not considered much of a threat in a general election. Recent polls though show Cox making it safely onto the November ballot.