MADISON, Wis. — A Republican Senate candidate in Wisconsin who calls himself "strongly pro-life" once sent a letter to a pro-abortion rights group praising its work and saying there was potential for a "strong partnership."

The letter is the latest record from Kevin Nicholson's time in 2000 as head of the College Democrats of America that is haunting him as he tries to win over conservative support for a Senate run. He also voiced his support for a "woman's right to choose" when he spoke at the 2000 Democratic National Convention.

Nicholson is running as a conservative for the seat held by Democrat Tammy Baldwin. He says he stopped being a Democrat years ago — after serving in the U.S. Marines, having children and working as a business consultant. He's likely to face one or more Republican opponents, putting a spotlight on Nicholson's positions on core conservative issues such as abortion.

His campaign spokesman Michael Antonopoulos downplayed the letter on Monday.

"It's pathetic to see Tammy Baldwin and her liberal allies dredging up decades old material from Kevin's college days," Antonopoulos said. "As the father of three children and a combat veteran who has seen innocent life destroyed, Kevin has made clear why he is strongly pro-life today."

Nicholson sent the letter via fax on June 28, 2000, to EMILY's List, a national Democratic group that helps raise money to support female candidates who support abortion rights.

Nicholson asked the political director of EMILY's List for a $10,000 donation, saying there was "great potential for a strong partnership."

EMILY's List president Stephanie Schriock was in Wisconsin on Sunday to attend a fundraiser for Baldwin. Schriock said the letter shows that Nicholson can't be trusted.

Schriock said Nicholson "knows he has a problem" with his change in position on abortion, which she attributed to "political expediency." The fact that Nicholson now says his previous support for abortion rights was a mistake should make women voters nervous, Schriock said.

"This is really about the voters of Wisconsin understanding when he stands," she said.

Nicholson, 39, has argued that because he chose to become a Republican after his life experiences, his beliefs are more solid than when he was younger and a Democrat. He touted his anti-abortion stance in his campaign launch video released last week.

"The one thing in life you cannot compromise are your principles," Nicholson said in the video. "I'm strongly pro-life. I've seen innocent children killed in Iraq and Afghanistan. And here in this country, it is unacceptable for our government to systematically allow the lives of innocent children to be taken."