LOS ANGELES — Voters headed to the polls in eight US states for key primary elections Tuesday, with all eyes on California, where the outcome could swing the balance of power in Congress.

Democrats in the country’s most populous state are battling to ensure they come out on top in several congressional districts that voted for Hillary Clinton over Donald Trump in the 2016 presidential election.

However, given the state’s unusual election system in which the two top vote-getters move on to the general election in November, regardless of party affiliation, Democrats fear they may give Republicans the upper hand in some districts where they have a glut of candidates.

Democrats splitting vote?

“The worry is that with so many enthusiastic Democrats running for Congress, the Democrats will split up the Democratic vote and you’ll end up with one or two Republicans in the top two slots,” said Elaine Kamarck, a senior fellow at the Washington-based Brookings Institution.

“So there’s quite a bit of concern that this would backfire and that congressional districts that would elect a Democrat in the end would be given only the choice of Republicans.”

The race has garnered huge attention nationwide, especially given how solidly Democratic California has been, but it is unclear whether the high stakes will spur voters to cast ballots.

“Turnout is always the uncertainty in primary elections,” said Louis DeSipio, a political science professor at the University of California at Irvine.

“If Democrats are as energized in California as they have been in some other states, they can move into the general election with no viable Republicans running statewide.

“This seems unlikely, but is a possibility.”

There are 27 candidates looking to succeed Democratic Governor Jerry Brown, and more than two dozen looking to replace veteran US Senator Dianne Feinstein.

And in the race for California’s 53 seats in the US House of Representatives, the slate of candidates features a plethora of novice Democrats looking to make a statement against Republican President Donald Trump and his anti-immigration, anti-environment policies.

Kamarck said that although Democrats in the most prominent anti-Trump states in the country would be expected to fare well, the “jungle” format of the election could create chaos.

‘High Crime Nancy Pelosi’

Trump tweeted early Tuesday to drive Republicans to the polls.

"Get the vote out in California today for Rep. Kevin McCarthy and all of the great GOP candidates for Congress. Keep our country out of the hands of High Tax, High Crime Nancy Pelosi," Trump said, referring to the 78-year-old House Democratic minority leader.

In the race for the governor’s mansion, former San Francisco mayor Gavin Newsom -- who gained attention for allowing same-sex unions before the legalization of gay marriage -- has a strong lead in opinion polls.

Former Los Angeles mayor Antonio Villaraigosa, also a Democrat, is in second place, but he could be outrun by Republican businessman John Cox, if other fringe Democratic candidates earn votes.

Some also think Villaraigosa has counted too heavily on the Latino vote, notoriously unpredictable in the primaries, and has failed to mobilize wider support.

In the Senate race, Feinstein is leading, followed by Democratic challenger Kevin de Leon, but the number of candidates in the race could throw a spanner in the works for the party.

In the House races, Democrats are focusing on seven districts currently in Republican hands that voted for Hillary Clinton in 2016 and could flip again this year.

But in at least five of them, progressive candidates could split the vote, leaving a path for Republicans to make the November runoff.

The Democratic Party “tried to winnow out some of the candidates, but the same excitement and energy that led them to run in the first place makes them unlikely to listen to the national party,” DeSipio said.

Polls close in California at 8pm (0300 GMT Wednesday).

Officials say the results in some key districts could take days or even weeks to come out, given that many Californians vote by mail.

Polling officials said they were receiving an unusually high number of mail-in ballots this year, making it more difficult to predict the final outcome.

Nationwide, Democrats must clinch at least 23 seats from Republicans to wrest control of the House of Representatives. — AFP