Friday marks the one year anniversary of the Supreme Court’s Citizens United decision giving corporations the right to make unlimited campaign ads—often without disclosing the donors who funded the ads. As a result of that decision, dark money spending to elect or defeat candidates in the 2010 midterms topped $450 million dollars, or about 15 percent of total spending on elections. But the spending is not over. An ironic result of the decision is that it requires the same groups that engaged in “electioneering communications” before Election Day to spend wildly on “issue ads” during the rest of the year.

Here’s how it works: Under IRS rules, a corporation that wants to hide the donors to its election activities and still maintain its tax-exempt status cannot have the election of candidates as its “primary purpose.” So it must spend more on “education” or issue ads than it spends on electioneering communications. That means, for example, that in order to keep its tax-exempt status, Karl Rove brainchild Crossroads GPS, which spent $17 million on campaign ads on the November elections, must now spend at least twice that on issue ads.

It has already begun. As my colleague Paul Blumenthal wrote here, Crossroads GPS recently spent $400,000 in twelve congressional districts, urging support for the extension of the Bush-era tax cuts. While ostensibly “educating” the public about the tax cut issue, the ads happened to be placed in districts held by Democrats who won their recent elections by the closest of margins. Is the group’s primary purpose “education” or “electioneering”? The line gets very blurry.

Make no mistake. Efforts to require groups to disclose who paid for their electioneering activities would not have required the disclosure of donors to issue advocacy campaigns. The Sunlight Foundation adamantly supports protecting the first amendment rights of groups to engage in true issue advocacy. But as a result of the Citizens United decision, special interests that directly impact elections with electioneering ads can augment their efforts by using issue ads to target vulnerable seats after the elections are over, all while disclosing nothing. Karl Rove and others taking advantage of the Citizens United case are most certainly celebrating the anniversary of the decision, probably by having cake. And eating it too.