The issue focused on an investigation by the federal Department of Justice's Office of Professional Responsibility that found there was "insufficient evidence" to file criminal charges against campaign workers.

It also includes information from a study conducted by an independent research firm, which showed about $4.5 million in funding for groups supporting Obama and other Democrats during the 2012 election came from companies with political ties.

But because of the studies' findings, Republican presidential candidates have turned up their efforts to connect their supporters to special interest