Rick Santorum has dropped out of the race for the Republican presidential nomination after running one of the most successful underfunded and unorganized campaigns. Perhaps the only campaign finance fact, however, that you need to know is this: Mitt Romney's super PAC spent more than $20 million attacking Santorum, while Santorum only raised $15.6 million through the end of February.The Center for Responsive Politics runs down Santorum's fundraising, which was pretty terrible until he suddenly became Romney's chief competition after the other, better financed candidates fell amidst a comedy of errors, sexual harassment claims, and "Oopses." CRP writes, "The former Pennsylvania senator's campaign raised $15.6 million, which ranks him sixth among Republican candidates -- far behind Romney, who has raised $74 million; Ron Paul, $34.1 million; Newt Gingrich, $20.7 million; and even former candidates Rick Perry, $19.9 million, and Hermain Cain, $16.8 million.