Sitting presidents often call upon former chief executives to raise relief money in the wake of natural disasters. But when President Barack Obama enlisted rivals Bill Clinton and George W. Bush to raise funds for Haitian earthquake victims, the effort went beyond the efforts of previous former presidents. The Clinton-Bush Haiti Fund leveraged unprecedented political unity and bipartisanship to raise $50 million — most of it in $10 donations made via text message — to help nearly 3 million victims of the Jan. 12 quake that killed nearly 260,000 people and destroyed 300,000 buildings in the poor Caribbean nation.