WASHINGTON (AP) — Democratic presidential candidates appealing to progressive voters with a call for “Medicare for All” are wrestling with the thorny question of how to pay for such a dramatic overhaul of the American health care system. Bernie Sanders, its chief proponent, says such a remodel could cost up to $40 trillion over a decade. But his rivals who support his plan have, so far, offered relatively few firm details about how they’d pay for it beyond raising taxes on top earners.