Governor Scott Walker says he’s keeping an eye on Wisconsin’s U.S. Senate race, but is not showing a preference for any of candidates seeking the Republican nomination.

The four-way GOP primary for the open U.S Senate seat has turned increasingly negative in recent weeks, with each of the candidates attacking the conservative credentials of others in the race.

The governor has said he would be a referee in the primary if the candidates get out of line. Following a heated debated in Green Bay on Monday, Walker says he “hasn’t dropped a flag yet, but it’s getting pretty close.”

Walker says he has not seen any blatant lies, although there are some questions about the interpretation of those attacks. The governor says he would like to see the candidates focus on their records and how they stand apart from the other candidates, heading up to the election.

Walker would not reveal who he plans to vote for, only saying he’s “watching closely” as one of the best primaries in the nation moves ahead. He says all four candidates would do an excellent job representing Wisconsin.

The GOP primary between former Governor Tommy Thompson, former Congressman Mark Neumann, Assembly Speaker Jeff Fitzgerald, and hedge fund manager Eric Hovde is August 14th.

AUDIO: Andrew Beckett reports (1:05)