Sen. Jon Tester, D-Mont., faces a potentially tough re-election bid. Win McNamee/Getty Images hide caption

itoggle caption Win McNamee/Getty Images

Former Massachusetts Gov. Mitt Romney gives a victory speech Tuesday in Novi, Mich., after winning the state's primary. Gerald Herbert/AP hide caption

itoggle caption Gerald Herbert/AP

Honda has a huge presence in Ohio, where the company and its suppliers are hiring. Here two advanced continuously variable transmissions undergo leak testing at the new assembly line at the Honda plant in Russells Point, Ohio. Ron Lietzke/AP hide caption

itoggle caption Ron Lietzke/AP