Not yet nominated Republican newcomer on Feingold's heels

It was supposed to be an easy re-election for Sen. Russ Feingold. And come November, it still may be. But for now, the Wisconsin Democrat is facing one of his toughest campaign challenges in a long and successful political career.

Polls show Mr. Feingold with a razor-thin lead over an unknown Oshkosh businessman with no political experience.

Although Republican Ron Johnson hasn’t even cleared his party’s primary, set for September, many in the Badger State say he poses a real threat to Mr. Feingold’s quest for a fourth six-year term in the Senate.

“Almost nobody knows anything about Johnson but yet he’s still only two to four points behind Feingold, and I think what that shows is just how energized Republicans are,” said Charles Franklin, a University of Wisconsin at Madison political science professor and co-founder of Pollster.com.