How an Abundance of Democratic Candidates Could Help the G.O.P. Hold the House

In a lesson in unintended consequences, a voting reform put in place in California could end up keeping Democrats off the ballot in two battleground districts.

SAN CLEMENTE, Calif. — This is Republican country, at least by California standards. But on a recent night, every folding chair set up in a tidy home on a suburban cul-de-sac was filled with a voter who wanted to meet one of the five Democrats running for Congress here.At first glance, the packed room — eight miles from what was once Richard Nixon’s Western White House — would seem an encouragi...