MADISON, Wis. — Ron Johnson says to control immigration the United States needs to secure its borders. Russ Feingold says the whole system needs to go.

Wisconsin’s U.S. Senate candidates are on opposite sides of the immigration debate. Johnson, a Republican, says the country needs to take a step-by-step approach, beginning by securing the nation’s border and removing incentives for illegal immigration before deciding what to do with the millions of people already in the U.S. illegally.

Feingold, a Democrat, says he supports comprehensive reform — rebuilding the system with a path to citizenship for people already here.

It’s unclear how immigration might factor in on Election Day. University of Wisconsin-Madison political scientist David Canon says immigration is hotter in southwestern states. Still, immigrant advocacy group Voces De La Frontera has endorsed Feingold.