For an example of the fluidity of campaign finance rules, as well as the tangled web of connections between candidates and super PACs, look no further than the digital consulting firm Targeted Victory.

So far, the firm’s hauled in $4.1 million working for Mitt Romney’s presidential campaign and American Crossroads, the super PAC launched by GOP strategist Karl Rove. Just down the hall, its neighbors in Arlington, Va., include an office housing four other companies working for Romney, American Crossroads or the pro-Romney super PAC Restore Our Future.

With the rise of super PACs, the jet-fueled political action committees that can take unlimited contributions, many campaign finance watchdogs have focused on the hundreds of millions of dollars being raised this presidential election cycle. But after the most recent campaign filings came in last week, ProPublica decided to track the other side of the equation: Where the money goes.

Our analysis found that more than $306 million has been spent so far by major super PACs and the five leading presidential candidates. In some cases, payees serve both candidates and the super PACs aligned with them, raising the specter that groups may be working together in ways that violate the rules, campaign finance experts […]