Why has the Wisconsin Senate race tightened?

A Marquette University Law School poll released Wednesday shows former Gov. Tommy Thompson (R) leading US Rep. Tammy Baldwin (D) 46 to 45 percent among likely voters in Wisconsin.

The US Senate race in Wisconsin, between former Gov. Tommy Thompson (R) and US Rep. Tammy Baldwin (D), is now in a dead heat. The polarization is true to the state’s political character, but what also might be playing a role is the neck-to-neck race between President Obama and Republican challenger Mitt Romney.

Mr. Romney’s bump in the polls follows a successful performance in the first presidential debate earlier this month. The tightening up of that race has been shadowed in key battleground contests like the one in Wisconsin.

While Ms. Baldwin had enjoyed a considerable lead in some polls since the primary in August, the race is now incredibly close, according to leading local polls. A Marquette University Law School poll released Wednesday shows Mr. Thompson leading Baldwin 46 to 45 percent among likely voters in Wisconsin.

The same poll shows that Wisconsin voters are as evenly divided regarding the presidential race: Forty-nine percent are supporting Mr. Obama and 48 percent are for Romney. Two weeks earlier in the same poll, Obama enjoyed a lead of 11 percentage points over his opponent.

Thompson is enjoying a “coattail effect” from Romney’s increasing poll numbers, but time will tell if it will help push him over the top, says Bruce Buchanan, a political scientist who specializes in presidential politics at the University of Texas in Austin.

“The [Romney] surge has not had enough time to take root yet. [Polling] is still up for grabs based on the second and third debates. Once those pass, if Romney is still competitive, it might be different,” Mr. Buchanan says.

Other surveys show a similar tightening for the Wisconsin Senate seat. A Rasmussen poll released last week shows Baldwin leading Thompson 51 to 47 percent among likely voters. Also last week, a poll conducted by Quinnipiac University, The New York Times, and CBS News shows Baldwin in the lead, 48 to 46 percent, among likely voters.

Wisconsin’s Senate race came to be after Herb Kohl (D), a four-term senator, announced his retirement. The seat has since become key to the Republican strategy of gaining control of the Senate, which explains heavy spending in the race by conservative “super political-action committees” such as Crossroads GPS and Americans for Prosperity.

Also affecting outside spending is the fact that Baldwin is openly gay. Although that has not been an issue in the campaign, it is helping drive donations from national liberal groups like MoveOn.org and the Gay & Lesbian Victory Fund. If elected, Baldwin, who has served in the US House of Representatives since 1999, would be the first openly gay US senator in history.

Baldwin is outraising Thompson, according to financial data released this week by both campaigns. Her campaign has raised $3.6 million since the primary, compared with $2.2 million by Thompson, who served as governor between 1987 and 2001 and was appointed Health and Human Services secretary under President George W. Bush.

But outside money represents the majority of donations, according to the Federal Election Commission, which says independent groups on both sides of the political spectrum have spent a total of $23.2 million on the race. By comparison, in the 2010 Wisconsin Senate race between newcomer Ron Johnson (R) and then-Sen. Russ Feingold (D), independent groups spent just $3 million. The majority of outside spending this time has been by groups attacking Baldwin.

The intensifying race has also been reflected in heated rhetoric on the campaign trail.

Thompson came under fire this week after he blasted Baldwin on Sunday for being “anti-Jewish,” referring to her votes in Congress against legislation sanctioning Iran. He later clarified that he meant to say she was “anti-Israel.”

While not related to the campaign directly, a video of Thompson’s son Jason also went nationwide Monday. In the video, Mr. Thompson is heard speaking at a fundraiser for his father where he tells the audience they have “the opportunity to send President Obama back to Chicago – or Kenya.” The remarks were interpreted as endorsing the “birther” movement, which has been largely discredited. The younger Thompson later apologized for the comment.

Thompson’s electability was once assured based on his name recognition and vast likability in the state as a moderate conservative dating back to his years as governor. That shifted during the Republican primary, when he took hard right positions that many perceived as catering to national trends in his party, says Dennis Dresang, a political scientist at the University of Wisconsin in Madison. Those positions helped Baldwin portray him early in the race as unreliable and dogmatic.

“Tommy looks bad,” Mr. Dresang says. “Voters are asking, ‘Who is this guy after all? Is he really the moderate guy, the problem solver, the pragmatic politician we knew in the past, or is he really someone pandering to the right wing?’ I think his new approach is backfiring and largely explains why this is race is so tight.”

Thompson and Baldwin are scheduled to debate Thursday in Wausau.

[Editor's note: The headline for this story, as well as the text, was adjusted to more accurately reflect the poll numbers for Baldwin and Thompson last month.]