Thompson led Baldwin in polls shortly after his narrow primary win in August, but a barrage of attack ads against him that went mostly unanswered vaulted her into a narrow lead. Now, with both candidates and the outside groups backing them spending heavily on the airwaves, the race seems to have settled into a tight contest.

President Obama leads Mitt Romney 50-47 percent in the same poll of 1,327 likely Wisconsin voters, which had a margin of error of 2.7 percent. The poll was conducted from Oct. 4 through Oct. 9, a period that began right after the Obama-Romney presidential debate.