Sign up for California Today for the latest news on the June 5 primary and more here.

IRVINE, Calif. — National Democrats, confronting mushrooming political chaos across Southern California, are pouring millions of dollars into congressional races to avert a self-inflicted disaster that could undermine their chances at taking control of the House.

After months of optimism that the state’s June 5 primary would position them to pick off seven Republican-held districts in November — a substantial down payment on reclaiming the House — Democrats are now trying to ensure that they do not hurt themselves because of their unusually crowded slates of candidates.

With so many Democrats running, the party’s fear is that the vote will be splintered, allowing Republicans — who have fewer candidates — to dominate some primaries. The party and allied groups are spending more than $4 million on just three campaigns, intervening in one contest to prop up a favored candidate; attacking a Republican from the right in another; and even reminding people not to waste their votes on “ghost candidates” who have dropped out yet remain on the ballot.

As any progressive activist will explain through gnashed teeth, the head-snapping scramble is because of the state’s “top two” open primary system, which allows the two leading vote-getters — regardless of political parties — to advance to the general election.