Republican state Sen. Leah Vukmir trails Democratic U.S. Sen. Tammy Baldwin by just two points according to a Marquette University Law School poll released Wednesday.
Baldwin leads Vukmir 49-47 percent among likely voters, but among registered voters, Baldwin is ahead by eight points.
Vukmir defeated businessman Kevin Nicholson in the Republican primary election on Aug. 14. Before her victory, 66 percent of voters said they didn't know enough about her to have an opinion. That's down to 48 percent now.
Among those registered voters who do have an opinion, 25 percent view Vukmir favorably, while 26 percent view her unfavorably.
Baldwin is rated favorably by 43 percent of registered voters, and unfavorably by 40 percent.
According to data compiled the Center for Responsive Politics, the Wisconsin Senate race is among the most expensive in the country, with nearly $40 million spent already by candidates and outside groups.
Vukmir campaign manager Jess Ward said in a statement that the poll results show that Baldwin is in "the fight of her life because she clearly represents the far-left of the Democratic Party supporting socialized health care, the Iran nuclear deal, and refusing to fund a border wall."
Baldwin spokesman Bill Neidhart said on Twitter that outside spending is keeping the race tight and competitive.
"Outside groups have spent more than $11 million against @tammybaldwin. The close #mulawpoll results are exactly what they were looking for as they gear up to spend more in the fall," Neidhart tweeted.
In a hypothetical matchup in June, before the primary election, Baldwin led Vukmir by nine points.