The parents of a GOP candidate for the US Senate in Wisconsin have made the maximum contributions allowed in the race — to their son’s rival.

Kevin Nicholson announced in July that he would seek the Republican nomination to challenge incumbent Sen. Tammy Baldwin in the 2018 midterm elections.

In December, his parents, Donna and Michael Nicholson, each donated the maximum amount — $2,700 — to Baldwin, CNN reported.

Nicholson said he’s not surprised his parents would contribute to Baldwin, since they’ve always backed Democrats.

“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,” he said in a statement to CNN.

​His parents are longtime backers of Democrats and Baldwin. ​

Donna Nicholson made 15 contributions totaling $441 to Baldwin’s campaign between 2012 and 2016, according to the Milwaukee Journal Sentinel.

S​ince her son threw his hat in the ring in July, she has contributed to Democratic candidates or causes 14 times, including to former Sen. Al Franken, who has since resigned over sexual misconduct charges, and ​Sen. Tim Kaine of Virginia, who ran on Hillary Clinton’s ticket as her vice president.

Nicholson, who in 2000 was president of the College Democrats in America at the University of Minnesota, said his shift from blue to red politics was gradual until he heard Democrats opposing the war in Iraq, where he served in 2007.

“I’m a conservative today not because I was born one, 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​,” he said.

“Regardless of who may disagree with my life decisions, I would not trade these experiences for anything, and they will always guide my views as Wisconsin’s next US senator.”

In 2000, when Nicholson was the president of the College Democrats of America, he told the Journal Sentinel that his parents might not like it if he ran for office in Wisconsin.

“They’re afraid of being found out as the only Democrats in Mequon,” Nicholson said at the time.

Donald Trump unexpectedly won Wisconsin in 2016, and Democrats have become increasingly nervous about Baldwin’s seat amid an onslaught from conservative groups.

By early January, nine groups had spent more than $4.7 million on ads that attack Baldwin or boost one of her Republican opponents, including Nicholson, according to her campaign.