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, ...