The House majority could be in the balance Tuesday when California voters head to the polls to pick nominees in some of the most consequential races up for grabs this year.

Their verdicts will offer early clues about the advantage Democrats hold heading into the midterm elections and whether Republicans can mitigate some of the damage by focusing on key issues.

Here are the seven storylines to watch when Tuesday’s results roll in:

Will Democrats shoot themselves in the foot?

The Democratic path to a majority in Congress runs through California, where seven GOP-held districts voted for Democratic presidential nominee Hillary Clinton Hillary Diane Rodham ClintonDemocratic groups using Bloomberg money to launch M in Spanish language ads in Florida The Hill's Campaign Report: Presidential polls tighten weeks out from Election Day More than 50 Latino faith leaders endorse Biden MORE in 2016.

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California’s "jungle" primary system advances the top two vote-getters to November’s general election, regardless of party affiliation.

That could work against Democrats this year, if crowded Democratic fields split the electorate in key House districts so much that two Republicans advance to the midterms.

That nightmare scenario is possible in three Republican-held districts, represented by Reps. Dana Rohrabacher Dana Tyrone RohrabacherDemocrat Harley Rouda advances in California House primary Lawyers to seek asylum for Assange in France: report Rohrabacher tells Yahoo he discussed pardon with Assange for proof Russia didn't hack DNC email MORE, Darrell Issa Darrell Edward IssaDCCC reserves new ad buys in competitive districts, adds new members to 'Red to Blue' program Wife of former Rep. Duncan Hunter sentenced to 8 months of home confinement Harris endorses Democrat in tight California House race MORE and Ed Royce Edward (Ed) Randall RoyceThe 'extraordinary rendition' of a US Presidential Medal of Freedom recipient, 'Hotel Rwanda' hero Gil Cisneros to face Young Kim in rematch of 2018 House race in California The most expensive congressional races of the last decade MORE. Democrats have poured millions into early television advertising designed to boost turnout and avoid a disastrous shutout.

In Rohrabacher’s Orange County district, Republican Scott Baugh could take the second slot for the general as two Democrats — businessman Harley Rouda and stem cell scientist Hans Keirstead — battle in a contest that pits national Democrats against the state party.

In Issa’s district north of San Diego, four Democrats and three Republicans are fighting for two slots in what may be the most uncertain race in the country. Doug Applegate, who lost to Issa by just 1,600 votes two years ago, and self-funder Sara Jacobs are the leading Democrats; Rocky Chavez and Diane Harkey are the most likely Republican front-runners. Recent polling shows Jacobs and Harkey with late momentum.

The race to replace Royce got so nasty last month that Democrats brokered a peace deal between businessman Andy Thorburn and philanthropist Gil Cisneros. Democrats have spent money attacking Orange County Supervisor Shawn Nelson and former state Sen. Bob Huff (R), while former assemblywoman Young Kim (R) lurks.

GOP’s top-of-the-ticket woes

In a year when all eight statewide offices and a U.S. Senate seat are up for grabs, Republicans face the grim prospect of being shut out of all but a few low-profile races.

In the race for governor, Lt. Gov. Gavin Newsom (D) leads the field by a comfortable margin. Two Democrats — former Los Angeles Mayor Antonio Villaraigosa and state Treasurer John Chiang — are competing with Republican businessman John Cox for the second position in the runoff.

Sen. Dianne Feinstein Dianne Emiel FeinsteinFeinstein 'surprised and taken aback' by suggestion she's not up for Supreme Court fight Democrats shoot down talk of expanding Supreme Court Biden leads Trump by 12 points among Catholic voters: poll MORE (D) is likely to face former state Senate President Kevin de León (D) in November. The runoff for attorney general is also likely to be a two-Democrat affair. And no Republican has even filed to run for insurance commissioner of superintendent of public instruction.

Without Republicans running in the most prominent races on the ballot in November, the party fears a deep drop-off in turnout that could impact GOP hopes of keeping key House and state legislative seats, exacerbating a Democratic edge in a year already friendly to liberals.

But Republicans may get a reprieve, at least in the race for governor. President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE endorsed Cox by tweet last week, and late polls show Republican voters coalescing behind the businessman-turned-politician. Republicans are hugely outnumbered in California, but the divided Democratic field could hand Cox the second slot in the runoff — and give Republicans reason to hope.

The future of the Democratic Party

The subtext in many of those competitive Democratic primaries is a fight over the future of the Democratic Party.

In several districts, more traditional Democratic candidates who have won endorsements from local and national party leaders are battling outsiders who scored backing from progressive groups.

The marquee matchup is in Orange County’s 45th District, where dueling law professors are racing for the right to face Rep. Mimi Walters (R) in November. Dave Min won the California Democratic Party’s endorsement, while the Progressive Change Campaign Committee (PCCC) and Sen. Elizabeth Warren Elizabeth WarrenDimon: Wealth tax 'almost impossible to do' CNN's Don Lemon: 'Blow up the entire system' remark taken out of context Democrats shoot down talk of expanding Supreme Court MORE (D-Mass.) are behind Katie Porter.

The peace deal between Thorburn, backed by Our Revolution, and Cisneros, favored by national Democrats, has de-escalated a fight that nonetheless represents a referendum on the party’s future — and whether Democratic voters will continue to stomach outside influence in a primary.

In the race to face Rep. Duncan Hunter Duncan HunterDCCC reserves new ad buys in competitive districts, adds new members to 'Red to Blue' program Wife of former Rep. Duncan Hunter sentenced to 8 months of home confinement Harris endorses Democrat in tight California House race MORE (R), the California Democratic Party, Our Revolution and the PCCC have settled on Ammar Campa-Najjar, a former Labor Department official. That represents a snub of Josh Butner, a local school board member once touted as a rising star and A-plus recruit.

The primaries have also raised a schism between state and national Democrats. In Rohrabacher’s district, national Democrats back businessman Rouda; the California Democratic Party voted to endorse Keirstead, a biomedical company CEO.

An early national clash

Special elections held over the last year have been marked by big spending from Republican groups and virtually nothing from the Democratic side. That’s all changed in California, where early Democratic spending reveals the priority the party places on top-tier races.

In recent weeks, the Democratic Congressional Campaign Committee (DCCC) has spent more than $4.5 million attacking Republicans in districts held by Royce, Rohrabacher and Issa — all Clinton districts in 2016. Most of that money has gone toward trying to divide Republican votes and help Democrats slip into the primary, but in the 48th, they are also running ads supporting Rouda, their chosen candidate in that crowded primary.

The DCCC has also built out a field organizing team in seven California districts; the party sees the Golden State as such a golden opportunity that it set up a satellite office in Orange County last year.

The National Republican Campaign Committee has its own California office staffed with organizers. And last week, it launched a six-figure digital ad buy to boost turnout in those same districts targeted with DCCC ads.

The competing field strategies — both aimed at bolstering turnout — will offer an early glimpse of each party’s relative intensity ahead of the midterms and the effectiveness with which the two sides are able to get their supporters to the polls.

Democrats’ 'Medicare for all' consensus

A vicious dispute over single-payer health care opened a deep rift between Democratic leaders in the state legislature last year. But among Democratic candidates for Congress, there seems to be a much more harmonious consensus over universal health care.

In the seven Clinton-won districts, an overwhelmingly majority of leading Democratic candidates support "Medicare for all" — or at least a pathway that would eventually lead to a single-payer system. That means most of the eventual Democratic nominees in those seven races are likely to favor a more liberal approach to coverage than even the Affordable Care Act achieved.

All four Democratic candidates running against Rep. Steve Knight (R) back Medicare for all. The same goes for Issa’s seat.

The rare candidate who doesn’t favor such a liberal position has even come under fire for his caution. That candidate is Min, the establishment-backed Democrat challenging Walters. The PCCC took shots at Min for distancing himself from the Medicare-for-all position, in contrast to their favored contender, Porter.

In a sign of just how far the Democratic Party has moved on what was once a third-rail issue, Min responded that he supports “many pathways to achieve universal health care coverage.”

How big is Feinstein’s edge?

When she first won election in 1992, Sen. Dianne Feinstein (D) was decidedly on the liberal side of the Democratic Party. A generation later, Feinstein’s views are much more mainstream — so much so that they anger some liberals who wish she would take more progressive stands.

Feinstein faces a challenge from de León, the former state Senate president, who amassed a fiercely liberal record in Sacramento.

De León has struggled to raise the money to compete with Feinstein, who loaned her own campaign $5 million in December. But the contest has split the state Democratic Party between established interests like the Human Rights Campaign and United Farm Workers, which back Feinstein, and progressive interests like Daily Kos, local chapters of Our Revolution and the California Nurses Association, which back de León.

Most public polls show Feinstein poised to earn somewhere around 40 percent of the vote on Tuesday, guaranteeing her a spot in the November general election. De León is polling just under 20 percent, according to a survey taken last month by the Public Policy Institute of California. Those polls show a vast majority of Californians have an opinion about Feinstein, while de León remains largely unknown.

(At least one survey, conducted online by the University of California, Berkeley, shows Republican James Bradley with a shot at winning the second slot.)

Is Feinstein vulnerable to a serious challenge from the left? If she can’t break 40 percent of the vote on Tuesday, look for progressive groups to make de León's campaign a top priority this year. But with so many other Democratic opportunities on the ballot this year, any sign of weakness from Feinstein’s challenger will virtually guarantee Feinstein another six years in the Senate.

The GOP’s gas tax gambit

For decades, California voters have trended to the left. But every now and then, the electorate decides it has been taxed enough, making life uncomfortable for Democrats who vote for tax hikes.

This year, Republicans are trying to create a similar backlash to a gas tax passed by the Democratic-controlled state legislature in 2017. Walters and a group of GOP strategists have been collecting signatures to force a vote on the gas tax, a strategy they hope will bring tax-weary Republican voters to the polls.

Tuesday’s elections will offer a preview of whether that strategy will work. Republicans have collected enough signatures to force a vote on whether to recall state Sen. Josh Newman (D), who voted for the $52 billion tax hike.

Newman represents a district that covers parts of Los Angeles, Orange and San Bernardino counties, where Clinton won by a 13-point margin. But Clinton’s edge belies the contours of an ordinarily conservative district: Newman became the first Democrat to win the seat in more than 20 years in 2016, when he bested a Republican assemblywoman by just 2,500 votes.

If voters decide to recall Newman on Tuesday, they will rob Democrats in Sacramento of the supermajority that gives them the ability to pass legislation without GOP input. They will also send a signal to state Republicans that the gas tax has become so deeply unpopular that it could mitigate some of the Democratic advantage heading into November.