An overlooked enforcement decision by the Federal Election Commission involving Senator John McCain’s 2010 campaign may put another type of player onto a campaign field that has become increasingly dominated by super PACs, nonprofits and non-candidate groups—other candidates’ campaigns.

The FEC announced last Friday that it found no reason to believe that McCain’s campaign broke the law by making independent expenditures against Representatives in 2010. You can see the McCain ads here and here. (Full disclosure: the present author drafted the complaint against McCain. This post represents his own views, and not any client’s.)

At issue was a statute—52 U.S.C. 30102(e)—that allows a candidate’s principal campaign committee to “support” only that candidate. (A narrow exception allows the campaign to make contributions of up to $2,000 to other candidates.) The Commission had aggressively enforced this statute before:

What seems to have saved McCain, apart from the FEC’s apparent slowness to enforce—his matter remained open for nearly five years—was Citizens United v. FEC. The Commission relied on that landmark case, which held that independent expenditures presented an insufficient risk of corruption to justify limits on their financing, and said: “It is unlikely that independent spending by authorized committees would be deemed more potentially corrupting than independent expenditures by individuals, political parties, or corporations, each of which has been found to have a constitutional right to make unlimited independent expenditures. Therefore, the Commission dismisses the allegation.”

The McCain decision is an odd case  involving a very odd statute. But it could have a significant effect on future elections. The decision makes clear that candidates face no legal barrier against making independent expenditures to support other candidates, so long as they do not coordinate with those whom they are supporting. This could prove significant especially in national elections, where Senate and House candidates are often eager to ally themselves with presidential candidates, as was the case in the Jenkins and Stupak matters. The decision could prove especially significant for nationally prominent candidates like McCain, who have a broad fundraising base and ample resources to spend.