Sen. Hillary Clinton called President Bush's homeland security plan a "myth" yesterday, charging that Americans are nearly as vulnerable to terrorism as they were before the Sept. 11 attacks. In her most scathing challenge to the President's domestic security efforts, Clinton said the White House has done little to prevent terrorism at home beyond "reorganizing existing bureaucracies." "Our vigilance has faded at the top, in the corridors of power in Washington ... where leaders are supposed to lead," she told a conference on homeland security at John Jay College of Criminal Justice on the West Side. "We are not prepared...