The map of key Senate races largely matches up with the map of presidential battlegrounds.

Aside from Wisconsin and Illinois, where Republican incumbent Sens. Ron Johnson (Wis.) and Mark Kirk (Ill.) are fighting for their political lives in blue states, the most competitive Senate contests are in presidential swing states. 

Johnson trails former Democratic Sen. Russ Feingold in Wisconsin by five points, according to a mid-August Marquette Law School poll, and Democrats predict Feingold will raise more money.

Republicans counter that Feingold is fighting against history by trying to oust an incumbent who defeated him six years earlier — something that hasn’t happened since 1934.

Kirk, meanwhile, lagged six points behind Rep. Tammy Duckworth (D-Ill.) in a late-July survey by Public Policy Polling, a Democratic firm.

But Republicans are playing up Duckworth’s primary challenge, which threatens to create a schism in the Democratic Party along racial lines. Her challenger, Andrea Zopp is African American.