The stakes for the 2014 midterm election are high. Just look at the cash flying around. As of one week from Election Day, this year had seen $694 million in outside spending—money spent by groups independently of campaigns, typically on broadcast ads attacking a candidate—nearly 50 percent more than any previous midterm through the same point. Thanks in part to Citizens United v. Federal Election Commission (2010) and other court cases, outside spending is the fastest growing source of money in politics, eclipsing direct contributions to candidates and parties.

(Click through for a larger image.)

The rise of outside spending might seem to threaten the power of the political establishment, since any “association of citizens” (as the majority opinion in Citizens United refers to them) can now spend unlimited sums on ads supporting or opposing candidates—or donate to a super PAC that will do the same. And, indeed, some major interest groups, such as the National Rifle Association and environmental organizations, as well as a handful of activist billionaires, most notably the Koch brothers, are among this cycle’s largest providers of outside money.

Many of the biggest sources of outside spending, however, aren’t outsiders at all. Several of the largest super PACs have close ties to party leadership, campaigns, or both. This cycle’s top-spending super PAC, Senate Majority PAC, is helmed by former advisors to Harry Reid; last cycle’s leader, American Crossroads, was founded by Karl Rove and features a board of directors composed entirely of former Republican Party operatives. Party-linked groups of this kind account for 19 percent of all disclosed outside spending this cycle, and traditional party organizations such as the Democratic and Republican National Committees another 29 percent. Additionally, the Center for Responsive Politics has identified eighty-seven super PACs devoted to electing a single candidate, many run by the candidate’s associates. In all, candidate-linked groups account for 8 percent of 2014’s outside spending. More than half the outside money this cycle is flowing either through parties or groups that are legally independent of parties and candidates yet are in fact adjuncts of them.

Whether you should be concerned about parties and candidates co-opting outside spending depends on which political problems you prioritize. Legal scholar Richard Pildes argues that allowing parties to command more resources increases their control over their members, perhaps helping to counteract polarization. But, by the same token, the fictive wall between candidates, parties, and supposedly independent spenders enables interest groups to write even bigger checks to political leaders, helping them earn gratitude—and perhaps influence—ever more easily.

Editor's Note: The online version has been updated to reflect changes. In addition, the print version reported that all party committees account for 75 percent of outside spending. The correct figure at the time of publication was 27 percent.