WASHINGTON — Tuesday, June 5, 2012, will be remembered as the beginning of the long decline of the public-sector union. It will follow, and parallel, the shrinking of private-sector unions, now down to less than 7 percent of American workers. The abject failure of the unions to recall Wisconsin Gov. Scott Walker — the first such failure in U.S. history — marks the Icarus moment of government-union power. Wax wings melted, there’s nowhere to go but down.