Primary election season is underway in many parts of the country. As Democrats and Republicans vie for their party’s endorsement for the general election, the primary results give observers and the parties insight into what voters think about the performance of their elected officials up to now, and what they want from them going forward. We can learn a lot from California. In that state’s primary election on June 7, voters sent a clear message to their elected officials — a message that the Democratic Party should take to heart if they want their candidates to compete effectively in November’s...