California voters eliminated traditional party primaries in 2010, replacing them with the top-two system at the urging of Arnold Schwarzenegger, a Republican governor, and other moderates. They argued that a primary open to all voters would lead to political moderation by candidates who, in theory, could not win by appealing only to the base of their party.

The voter initiative was vigorously opposed by Democratic and Republican leaders who warned that it would force candidates to invest time and money in debilitating primaries and runoffs, and could lead to general elections where a major party would be kept off the ballot.

It is far from clear whether the top-two system — which has been adopted in some form by four states so far — has lived up to its promise of good government reform, or created the kind of one-sided general elections that so concerned party leaders. That has happened in California in a congressional race in 2012, where there was a general election…

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