A late spending frenzy has broken out in California’s pivotal 48th District Congressional race as the leading Democratic challengers look to advance past Tuesday’s primary. And one candidate — Ammar Campa-Najjar — is the overwhelming target of the last-minute barrage. He has had millions more spent against him than any other candidate in the field. With four days left in the race, these groups will likely spend even more. Campa-Najjar had half-a…