___METHODOLOGY These rankings by The Associated Press, based on campaign financial reports submitted to the Federal Election Commission, include contributions to super PACs, presidential campaigns, political parties and joint-fundraising committees. Federal law limits maximum contributions to campaigns, parties and affiliated committees, but federal court rulings have stripped away such limits to super PACs. This analysis excludes secret but legal contributions that might have been made to nonprofit groups, which can pay for so-called issue ads that don't explicitly advocate for or against a candidate. Such groups are not required to identify their donors. Where available, the analysis considered donations "bundled," or raised, from other wealthy donors for Romney and President Barack Obama. Obama periodically identifies his bundlers, but Romney has resisted calls to do the same.