Wisconsin Gov. Scott Walker (R) does not plan to endorse any of the four candidates seeking the Republican nomination for the state’s open Senate seat. Instead, he’ll act as a neutral arbiter.

“It allows me to play a little bit of a referee and call out the candidates if they’re stretching the truth about the views of other candidates,” Walker told reporters today during a breakfast hosted by the Christian Science Monitor.

Walker praised the candidates and described the November Senate election as “a great chance” for Republicans to win a Senate seat regardless of who emerges as the GOP nominee. He referred to likely Democratic nominee Rep. Tammy Baldwin (D) as among the nation’s most liberal politicians.

“I’m excited,” he said. “It’s probably the most impressive primary, at least this cycle, if not one of the most impressive ever. I mean you’ve got four legitimate candidates.”

Walker, who has received national attention for his efforts to reform collective bargaining in Wisconsin and his easy victory in a gubernatorial recall election last week, also chimed in on Mitt Romney’s campaign for president, offering the presumptive GOP nominee advice on how to win Wisconsin in the fall.

Walker said that it would be a mistake if Romney “looks at Wisconsin and thinks that he can win just because I have an ‘R’ next to my name and he has an ‘R’ next to his name” — a line the governor has repeated several times since his June 5 victory.

Rather, Walker said that Romney would need to portray himself as a reformer with a plan to solve the country’s problems.