How bad does the public school system have to get before people see vouchers as the cure?

What will it take before people embrace school vouchers as the best cure so far to fixing the school system, do the public system have to go bankrupt? Do US students have to test in the lowest 15 nations of the world in basic 3 Rs? Would 3 out of every 5 schools have to close for lack of money? Will it take people to lower their fear that vouchers will make schools in affluent neighborhoods richer and poor neighborhood schools lacking, when that will not be the case? Before vouchers are applied universally across the board how bad will the schools have to get?