“Mayor de Blasio’s preliminary budget sets aside $50 million to have taxpayers guarantee an eye-popping 8.25 percent return on a special pension fund covering more than 20,000 school principals, supervisors and staffers. This supplemental fund is on top of the regular pension educators receive from the city, also guaranteeing a 7 percent return. … But here’s the difference — the taxpayers are on the hook even if the investments tank — guaranteeing 8.25 annual return for supervisors and 7 percent for teachers.”