For GOP lawmakers who view public education as a quasi-socialist project, the gaping hole in state budgets left by subsidizing private school tuition is a feature, not a bug. Bait-and-switch is an old retail tactic. You lure customers in with promises of a deep discount, only to inform them that the deal has a catch. The real price tag, it turns out, is quite a bit more. Though it took supporters of school vouchers a while to catch on, they’ve learned quickly that the trick works just as well in education policy as it does in retail sales. Pick a...