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US political scientists are usually busy in early August, polishing proposals for grants from the US National Science Foundation (NSF). But not this year.

Less than one month before an annual mid-August application deadline, the funding agency has scrapped new political-science funding for the rest of 2013. The NSF declines to explain its reasons for eliminating the grant call, one of two that typically take place each year. But leaders in the field are blaming Congress, which on 21 March passed a bill requiring that NSF-funded political-science research benefit either national security or economic interests.

“It’s hard to imagine that it’s not a factor in the decision,” says Michael Brintnall, executive director of the American Political Science Association in Washington DC, who describes the funding cut as “troubling”. Brintnall says that the NSF notified him about the cancellation on 25 July. Other calls for funding in the NSF division of social, behavioural and economic sciences — which includes political science — are continuing as usual.

The NSF’s decision removes one of the main financial lifelines for political-science research. “This is somewhere between devastating and crippling,” says Henry Farrell, a political scientist at George Washington University in Washington DC and an author of the Monkey Cage, a widely read political-science blog. But Farrell blames the political climate rather than the funding agency for the cut. “The NSF is in an extremely awkward situation,” he says.

The requirements for NSF political-science spending came during eleventh-hour negotiations for the 2013 omnibus spending bill. Some of the law’s language, proposed by Senator Tom Coburn (Republican, Oklahoma), prevents the NSF from “wasting federal resources on political science projects, unless the NSF Director certifies projects are vital to national security or the economic interests of the country.”

Since then, NSF officials have struggled to translate that language into rules for evaluating grant proposals and spending its roughly US$10-million budget for political science. On 7 June, the agency said that peer-review panels would take into account the extra requirements in their evaluation of grant proposals. But the cancellation of the August funding call suggests that the agency buckled under the uncertainty of how to interpret the law's stipulations, says John Aldrich, a political scientist at Duke University in Durham, North Carolina.

John Hart, a spokesman for Coburn, says that he is uncertain whether Coburn’s efforts can be linked to the NSF’s decision. But Coburn has vocally supported getting rid of political-science funding altogether. On its website, the NSF cites budget uncertainties as the reason behind its decision. NSF spokeswoman Deborah Wing declined Nature's request to interview Brian Humes, a political-science programme director, and she would not answer questions about the cancelled grant cycle.

The agency’s website says that it will hold its call for political-science proposals in January as usual. Aldrich says that this suggests that the funding shutdown is a response to the Congressional requirements, which are set to expire on 30 September — the end of the 2013 fiscal year. Avoiding the August funding round may be a strategic move by Humes to see whether the constraints disappear when the next spending bill is passed, says Aldrich. “If he can save the money and spend it later when there’s more clarity, that would be helpful,” Aldrich says.

Other researchers agree. “I think they’re probably worried about upsetting Congress,” says Rick Wilson, a political scientist at Rice University in Houston, Texas, and editor of the American Journal of Political Science. “So why not pull the plug rather than risk it?”