Who is the least effective Democrat in the U.S. Senate? Sen. Joe Donnelly, according to the Center for Effective Lawmaking, who said the Democrat from Indiana was the worst in his party at advancing agenda items toward becoming law during the last Congress. The nonpartisan center, run jointly by UVA and Vanderbilt University, creates effectiveness scores for each lawmaker in Congress based on 15 metrics, including how many bills a legislator sponsored and how far bills progressed toward becoming law.