A new study by the American Enterprise Institute -- "Do Political Protests Matter? Evidence From The Tea Party Movement" -- finds that the movement boosted Republican turnout by three to six million votes in the 2010 election. This effect was blunted in the 2012 election, though, because growth in the movement stalled.

That slowdown happened, co-author and AEI economist Stan Veuger notes, at the same time that the IRS began coming down hard on these groups. He argues in a RealClearMarkets.com article that this most likely had a major impact in the 2012 election.

"The founders, members, and donors of new Tea Party groups found themselves incapable of exercising their constitutional rights, and the Tea Party's impact was muted in the 2012 election cycle," Veuger said.

He added: "The data show that, had the Tea Party groups continued to grow at the pace seen in 2009 and 2010, and had their effect on the 2012 vote been similar to that seen in 2010, they would have brought the Republican Party as many as 5 to 8.5 million votes compared to Obama's victory margin of 5 million."

Given those numbers, it is reasonable to be suspicious of the IRS targeting, Veuger said.

The AEI study was done by Veuger, Andreas Madestam of Stockholm University, and Daniel Shoag and David Yanagizawa-Drott, both from the Kennedy School of Government at Harvard.