Last July, 2,000 conservatives and Tea Party activists gathered in Las Vegas for the annual FreedomFest, which featured GOP presidential frontrunners Donald Trump and Marco Rubio. But it was a fourth grade public school teacher from Orange County named Rebecca Friedrichs who promised the far right a prize that neither Trump nor Rubio could offer. Friedrichs and nine other California school teachers are part of a lawsuit now before the U.S. Supreme Court that could deliver a severe blow to the nation’s public-sector unions. It would radically upend the political power of labor — and also, conservatives hope, of the Democratic Party — across the United States.