When your parents donate to your political opponent

— -- One way for your parents to show they disapprove of your political aspirations is to donate -- to your opponent.

That's exactly what the parents of Wisconsin GOP Senate hopeful Kevin Nicholson did, maxing out donations to his Democratic opponent, Sen. Tammy Baldwin, according to Federal Election Commission records.

Just months after their son announced his campaign to unseat Baldwin, Donna and Mike Nicholson each gave her $2,700 -- the maximum amount legally permitted per election.

One person who wasn't surprised: Kevin Nicholson.

“My parents have a different worldview than I do, and it is not surprising that they would support a candidate like Tammy Baldwin who shares their perspective,” Nicholson said in a statement provided to ABC News.

Nicholson, a relative newcomer to Republican politics, has been open about his ideological evolution, including his upbringing in a Democratic family and even his past as president of the College Democrats of America.

“I’m a conservative today not because I was born one," Nicholson said, "but because of the experience I earned as a Marine in combat, my experience as a husband and father, my choice to be a Christian, the schools I chose to attend and the decision to pursue the career that I have.”

His mother, Donna Nicholson, has been just as committed to her liberal leanings, making several hundred small and mid-sized donations totaling more than $10,000 to Democratic candidates and PACs over the last 10 years.

And this is not the first time she has supported Baldwin: She donated more than $400 to her between 2012 and 2016, but nowhere near the $5,400 she and her husband donated in December.

Democrats tracking the race closely tell ABC News the political tension between family members -– playing out on the national stage -- raises questions about when and how Kevin Nicholson became a Republican and how he's connected with some of the biggest Republican mega-donors.

Some Republicans have questioned Nicholson's loyalty after he was caught on tape a few months ago criticizing House Speaker Paul Ryan.

Once backed by former Trump adviser Steve Bannon, Nicholson seems to have locked up unlimited support from Richard Uihlein, the founder of Wisconsin-based shipping company Uline. He has already funneled millions of dollars into pro-Nicholson outside groups, his aggressive spending helping to make the Wisconsin Senate race one of the most expensive so far this year.

Early in the election cycle, Uihlein dropped checks totaling $3.5 million to fund a pro-Nicholson super PAC called Solutions for Wisconsin. The super PAC has spent $209,056 to support Nicholson. Two other outside groups, also primarily funded by Uihlein, Americas PAC and Restoration PAC, have spent $1.9 million and $1.6 million respectively either in support of Nicholson or against Baldwin.

All told, super PACs and political nonprofits have spent more than $5.7 million in the Wisconsin Senate race so far this election cycle, all of it for Nicholson's benefit.

Baldwin, however, has been a prolific fundraiser in her own right. The Democratic incumbent raised a total of $2.8 million in the last quarter of 2017 and started this year with nearly seven million in her war chest. Nicholson’s campaign has only collected $801,201 during the same period, leaving him with just a little more than half a million to spend and $40,256 in debt.

ABC News' MaryAlice Parks and John Verhovek contributed to this report.

This story is part of "18 for ’18" – ABC News’ powerhouse coverage of the 2018 midterm elections.