Independent groups campaigning for various candidates have spent almost $2.2 million since the beginning of November. “Mobilization efforts matter, said Anthony Corrado, an expert on presidential politics at Colby College in Maine. That’s particularly true in Iowa, he said, where just a small fraction of the state’s population typically show up for the caucuses. With the candidates ‘fighting over just hundreds of votes on both sides of the aisle, these groups will have an effect,’ he said.”