Democrats redrew California's map to counter Trump. The primary tests whether it pays off for them

California Democrats persuaded voters to let them redraw the state's congressional map so the party could potentially gain five seats in the U.S. House to counter GOP redistricting in Texas . Tuesday’s primary will be the first indication of whether that will pay off.

The state’s unusual primary system, in which the top two vote-getters advance to the general election regardless of party, means Democrats have a chance of effectively missing out on a pickup in the San Diego suburbs, where Republican Rep. Darrell Issa's district was redrawn to give it a slight Democratic lean.

Issa retired, and a Republican San Diego County supervisor, Jim Desmond, stepped in to run. So did an avalanche of nine Democrats — so many that some fear the Democratic vote will be split among them, leaving Desmond and the only other GOP candidate, Jim O’Neil, as the top vote-getters. Under that scenario, Democrats would be locked out of the November general election.

“After millions of dollars and a nationwide effort to redraw these districts in response to Texas, Democrats being shut out would be a nightmare,” said Ammar Campa-Najjar, a former Obama administration official who is one of the Democrats running.

California has been the bright spot for Democrats in a redistricting war kicked off by President Donald Trump to help his party retain control of the House. After Texas redrew its map to make as many as five more seats winnable for the GOP, California voters allowed Democrats to suspend their state’s own independent redistricting commission and create a new map in retaliation.

But when Virginia Democrats tried to replicate that, they were blocked by their state Supreme Court . Meanwhile the conservative majority on the U.S. Supreme Court gutted a key provision of the Voting Rights Act , letting Republicans eliminate some majority-Black congressional districts in the South.

Campa-Najjar, San Diego City Councilwoman Marni von Wilpert and investor Brandon Riker, who is financing his own campaign, are the most prominent Democrats in the race for the seat vacated by Issa. Many Democrats are optimistic their voters will coalesce around one candidate and set up a competitive election against Desmond in the fall.

The 48th district would not be the only competitive fall race for Democrats.