MADISON, Wis. — The Latest on reaction to Kevin Nicholson comments about Democratic veterans (all times local):

4 p.m.

Republican Senate candidate Kevin Nicholson refuses to back down from recent comments he made about military veterans that have drawn a bipartisan backlash.

Nine Republican veterans who support Nicholson's primary challenger Leah Vukmir on Thursday called for Nicholson to apologize for comments he made during a debate last week.

Nicholson spokesman Brandon Moody said Thursday that Nicholson was calling out Vukmir for running a campaign that questions his personal character, which includes being a Marine.

Moody says Nicholson's service in the Marines as a captain who earned a Bronze Star is a "pretty damn good track record."

On Wednesday, Nicholson questioned the "cognitive thought process" of veterans who decide to become Democrats. Nicholson said Thursday that while he respects Democratic veterans, he doesn't understand how people can vote for them when they "routinely demean and belittle" the Constitution.

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2:50 p.m.

A group of Republican military veterans are calling on GOP U.S. Senate candidate Kevin Nicholson to apologize for inferring his service shielded him from criticism about his past as a Democrat.

The call came a day after Nicholson questioned the "cognitive thought process" of veterans who decide to become Democrats.

The nine veterans who sent Nicholson a letter Thursday all support his opponent in the race, state Sen. Leah Vukmir. The signers include Senate Majority Leader Scott Fitzgerald and state Rep. Ken Skowronski.

Nicholson did not immediately respond to a request for comment.

The veterans called for Nicholson to apologize for saying in last week's debate that his military service doesn't mean much to "certain politicians" in response to Vukmir's criticism of him formerly being a Democrat.

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2:18 p.m.

Republican U.S. Sen. Ron Johnson says he's going to leave it up to the voters to decide what to make of GOP Senate candidate Kevin Nicholson's disparaging remarks about Democratic veterans.

Nicholson is a former Marine who on Wednesday questioned the "cognitive thought process" of military veterans who decide to be Democrats.

The remarks have generated criticism from a wide array of Democratic veterans, including candidates for Congress in Wisconsin. But Republicans have largely been silent.

Johnson said in an interview Thursday that "I value all of our veterans, they are the finest among us."

As to whether he agreed with Nicholson or thought he should apologize, Johnson says, "I'll let the voters make their own judgment."

Nicholson faces state Sen. Leah Vukmir in the Aug. 14 primary.