(CNN) Few Democrats anywhere present themselves as more inveterate opponents of Donald Trump than California Lt. Gov. Gavin Newsom, the clear front-runner for the Democratic gubernatorial nomination in next week's primary.

And yet few Democrats anywhere are facing more pointed accusations than Newsom of pursuing a strategy that could help Trump achieve his highest political goal in 2018: maintaining Republican control of the US House.

The charge against Newsom, which his camp forcefully rejects, underscores how profoundly the dynamics of California's unusual top-two primary system distort the typical calculations for candidates and the two major parties.

One week before the June 5 vote, California Republicans face the near-certainty of failing to advance a candidate to the general election for US Senate, and the risk, though fading, of failing to place a candidate on the November ballot for Governor. Democrats, meanwhile, are terrified that they will be shut out next week in one or more Republican-held US House districts, particularly in suburban Orange County. Party strategists see winning these seats as key steps in their path back to majority control.

The two anxieties collided when Newsom ran an ad earlier this month effectively bolstering the leading Republican gubernatorial candidate John Cox. By promoting Cox, Newsom reduced the odds that he would face another Democrat in November and increased his own chances of victory. But he faced complaints that he was threatening Democratic hopes of recapturing the US House because a Republican in the governor's race would give California GOP voters more reason to turn out this fall and thus benefit their candidates for the House.

"There are all kinds of unintended consequences that are coming out now," says Mark Baldassare, president and CEO of the non-partisan Public Policy Institute of California.

An experiment that may have backfired

Under the new system, approved by California voters in a 2010 ballot proposition, the top two finishers in the primary for each office --from governor to US Senator, and US House to the state legislature-advance to the general election, regardless of party. The plan's supporters initially sold it as a way to promote more moderate candidates, to empower independent voters, and to weaken the hold of the two major parties on the electoral process. But in fact, the complex geometry of these open contests has encouraged a new peak of partisan maneuvering and manipulation, and forced each party to systematically intervene to try to influence the selection of the other side's nominees. As a senior adviser to one statewide California candidate put it: "It is constant three dimensional chess you are playing here."

Though the state has run three previous elections under the top-two rule, this is the first contest that is fully pressure-testing the system. In 2014, the one previous governor's race conducted under these rules, incumbent Democrat Jerry Brown cruised to re-election. And in the past three elections, Democrats inexplicably failed to mount serious bids against House Republicans in several districts that were trending away from the GOP.

But this year, the open governor's seat has drawn four serious Democratic candidates and two Republicans. In the House, after years of torpor, Democrats are fielding a flood of candidates in five Republican-held House seats around Los Angeles that Hillary Clinton carried against Trump in 2016. Those seats, as well as two other Republican-held seats in the agricultural Central Valley that Clinton carried, are vital to Democratic hopes of recapturing the overall House majority.

Under this heightened pressure, the top-two system has unquestionably sprung some leaks.

A local failure could have national consequences

Most attention has focused on the Democratic dilemma in Orange County. The Democrats began this year with high hopes in the four seats that Clinton carried across that steadily-diversifying county. But they now face the real risk that Republicans will claim both of the top spots and shut out Democrats for November in three of them. In descending order of threat, Democrats are confronting that possibility in the seat held by Rep. Dana Rohrabacher and the districts being vacated by retiring Republicans Ed Royce and Darrell Issa. (Because there are no meaningful Republican challengers to GOP incumbents Mimi Walters in Orange County and Steve Knight north of Los Angeles, Democrats don't face that risk in those Clinton-won seats.)

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In all three of the seats where Democrats face a potential shutout, Republicans have candidates with much stronger resumes in elected office, from former state Assembly member Young Kim and Orange County Board of Supervisors member Shawn Nelson in Royce's seat; to former State Assembly GOP Leader Scott Baugh, who is challenging Rohrabacher; to former Assembly member Diane Harkey and current member Rocky Chavez in the Issa seat. None of the leading Democrats contending for any of the seats hold elected office, or began the race with much name identification in their districts -- a remnant of the party's long-time failure to invest in building its support in Orange County. That's made it tougher for any one candidate to consolidate support.

This local failure has forced the national Democratic Congressional Campaign Committee into extraordinary exertions to avoid losing these seats to the GOP in June. The party committee has invested heavily in voter registration and get-out-the-vote efforts to combat the traditionally low turnout of several key Democratic constituencies during the June primaries. It has successfully leaned on several lower-tier Democratic candidates to drop out, hoping to consolidate the Democratic vote.

Most dramatically, it has invested $3.5 million into an array of television and radio ads meant to lift a Democrat into the top two. That's included negative ads trying to weaken Republican candidates in each race (principally Baugh, Nelson and Chavez). More controversially, the DCCC has also tried to lift one Democrat from the field by running ads for Gil Cisneros, a lottery winner and philanthropist in the Royce seat, and Harley Rouda, an attorney and entrepreneur in the Rohrabacher district.

And yet even after all this work, Democrats are still biting their nails. The Democrats are especially on edge about the Rohrabacher seat, where the incumbent's weakness is leaving a large number of GOP-leaning votes available to Baugh.

"These are all within the margin of error, and that's what is so scary," said Democratic consultant Dave Jacobson, who is advising candidates in the Royce and Rohrabacher seats.

The maneuvering in the governor's race is adding to Democratic anxiety and uncertainty. It has raised the possibility that even if Democrats survive next week's challenge and place a candidate onto the general election ballot, the Republican odds of holding the Orange County anyway seats may be rising.

Grumbling about Newsom's maneuvers

California Lt. Gov. Gavin Newsom on stage at The Beverly Hilton Hotel on November 19, 2012

Newsom triggered the controversy earlier this month when he ran his ad criticizing Cox, an underfunded San Diego business executive who lost several races for office while living in Illinois, for being too close to Trump and too opposed to gun control.

That's the sort of message viewers might expect from Newsom, a liberal Democrat, in the general election. But airing during the primary, the ad, in effect, came with a big wink: by attacking Cox from the left, Newsom was actually bolstering his credentials with Republican voters and increasing the chances that Cox would finish second next week ahead of any Democrat in the race. Newsom reinforced the message last week when he launched separate attack ads targeting Democrats Antonio Villaraigosa, the former Los Angeles mayor, and state Treasurer John Chiang.

Villaraigosa and Cox are the two candidates with a realistic chance of finishing second to Newsom, who leads comfortably in all polls. And even some Villaraigosa supporters privately now give him little chance of overcoming Cox, who was also boosted among Republicans by an endorsement from Trump. (In recent polls, Cox has pulled away from a second Republican, Travis Allen, who has run to his right.)

With Republicans dwindling to about a quarter of the state's registered voters, Newsom would begin the general election as a prohibitive favorite against Cox.

But Newsom has frustrated Democrats who believe the party would be more likely to beat the vulnerable GOP House members if Republicans are shut out of the governor's race. That, the critics argue, would depress GOP turnout, partly because Republicans are already virtually certain to be excluded from the US Senate race, which will likely feature incumbent Democrat Dianne Feinstein against State Senate leader Kevin de Leon. Delaine Eastin, a liberal former state superintendent of instruction also seeking the gubernatorial nomination as a Democrat, surfaced this grumbling last week, when she tweeted: "It is clear that for all of @GavinNewsom's claims to oppose @realDonaldTrump - he has put himself ahead of @TheDemocrats fight to take back Congress and win other down ballot races."

It is clear that for all of @GavinNewsom's claims to oppose @realDonaldTrump - he has put himself ahead of @TheDemocrats fight to take back Congress and win other down ballot races. https://t.co/QnGak9SkJd — Delaine Eastin (@DelaineEastin) May 25, 2018

Many Republicans actually take the same view. John Thomas, a Republican consultant, says the impact on Republican turnout could be catastrophic for GOP House candidates if the party is excluded from both the governor and US Senate races. "Our models it would probably change turnout by three points and that might just be it," says Thomas, who is working with Republican candidates in Orange County. "Barring a black swan event in some of those Congressional seats, with a Democrat imploding, a three-point shift [in turnout], is probably untenable."

Newsom has said openly he'd prefer to oppose a Republican this fall. But his advisers forcefully rebut the notion that he's advancing his own interests over the party's.

Nathan Click, Newsom's spokesperson, offers several interlocked arguments for why Democrats could benefit from a traditional intra-party match up in the governor's race. Among them: a Democrat vs. Democrat race would siphon away too much money from party donors who could otherwise contribute to down-ballot candidates; a race between two Democrats would widen party divisions, like the Hillary Clinton-Bernie Sanders contest, and potentially depress turnout; and a traditional Democrat vs. Republican race would allow Newsom, a prodigious fundraiser, to coordinate turnout and fundraising programs with the party, benefiting all Democrats on the ticket. As for the fear that a Republican in the governor's race would encourage more turnout in the contested Southern California House seats, Click says, "Regardless of what's at the top of the ticket, Donald Trump and the national dynamics are going to define what happens in those House races."

Those are all plausible arguments. But so is the belief that without a Republican on the ballot for either of the top two offices, "it would be logical that some Republicans are going to find it less important to vote," says Bill Carrick, the longtime top strategist for Feinstein.

No perfect system

The real issue for California voters and party strategists is not so much who is right, but why it is appropriate to be asking these questions at all. It's true that candidates across the country have grown increasingly aggressive about trying to influence the nomination process on the other side, but the top-two system in California has raised these interventions to an unmatched scale. It's not clear how either side benefits from a system that so powerfully encourages gaming the process during the primary, and potentially leaves millions of voters from each side without a choice representing their views in the general election.

Many observers in both parties foresee a potential effort to undo the system after this election. But while the top-two system passed with only a relatively narrow 54% margin, Baldassare cautions that, "I think it's very hard to repeal things that voters have passed." Recent state polls have found the system remains popular, but that could change quickly, if Democrats are shut out in one or more of the Orange County seats and that contributes to a failure to regain the US House.

Even that prospect has begun to stir discussions about revamping the system. "I think there are people who are talking about it," says Carrick. "What replaces it is probably a big debate." That debate could grow a lot more urgent in both parties depending on next Tuesday's results.