NBC News “First Read” listed the Wisconsin GOP Senate Primary in August as one of the ten primary contests to watch:

There’s a ton of outside money already pouring into Wisconsin as state Sen. Leah Vukmir (who’s been endorsed by Scott Walker’s wife Tonette) and Marine veteran Kevin Nicholson (who has the backing of the Club for Growth and megadonor Richard Uihlein, among others) battle for the chance to take on vulnerable Democrat Tammy Baldwin.

Baldwin was recently on MSNBC complaining that the Koch Brothers were responsible for her low approval ratings.

“Wisconsin has seen more outside spending, more super PAC spending, particularly from the Koch brothers,” Baldwin told MSNBC. “These out-of-state special interests think they own Wisconsin, and they’ve been attacking me, and that certainly contributes to how people feel about politics.”

Eric Bott, state director for the Koch-backed Americans for Prosperity (AFP), said on Twitter that Baldwin may want to look in another direction for her low approval rating.

“Perhaps she should take personal responsibility for her failures to fix the VA and policy positions that are far out of line with Wisconsin values,” Bott said.

In a recent Marquette University Law School poll, Baldwin had an unfavorable rating of 39 percent and a favorable rating of 37 percent. The poll also shows a slight drop in support from the same time last year when Baldwin had a 40 percent favorable rating and a 35 percent unfavorable rating.

The same poll showed Nicholson leading in the race over Vukmir, 28 percent to 19 percent. However, a plurality of GOP voters, 49 percent of them, were still undecided.

Businessman Eric Hovde, who previously ran in the Republican U.S. Senate primary in 2012 and finished second, is also considering entering the race.