If Matt Mahan didn’t exist, California Democrats would need to invent him. Mahan, the moderate Democratic mayor of San Jose, has long positioned himself as a foil to the — sometimes progressive, often will-of-the-wisp and increasingly national — politics of Gov. We know that many Southern Californians don’t know San Jose, even though it is the third-largest city in the state, trailing only Los Angeles and San Diego. So far, Mahan is leading with a back-to-basics approach that is sure to to resonate with Californians across the political spectrum. But, quite clearly, in a state that will likely elect a Democrat as governor, his candidacy is so far compelling.