A Republican U.S. Senate candidate in Wisconsin on Monday called his parents’ decision to support his Democratic opponent “an intentional personal blow” and a “true representation” of political intolerance. Wisconsin GOP Senate candidate Kevin Nicholson slammed his own parents for making the “maximum contribution” to his Democratic opponent in a fiery editorial published by Fox News

The hopeful who is currently embroiled in an intense primary battle for the GOP nomination accused his parents of turning “their back on me, my wife” and their grandchildren following a report from CNN earlier this year that highlighted his parents’ donations to the incumbent Sen. Tammy Baldwin (D-Wis.)

The column comes after a new attack ad from a group supporting his Republican opponent questioned whether Nicholson, a former Democrat, could be trusted. The ad used footage of Nicholson speaking in support of abortion rights at the 2000 Democratic National Convention. Nicholson’s primary challenger, Republican state Sen. Leah Vukmir, argues she’s the only true conservative in the race. The primary is a month away on Aug. 14.

He pointed to his parents’ donation as a “representation of the intolerance” in the Democratic Party.

“Adding to this, they decided to make the maximum contribution to my Democrat opponent in my campaign for U.S. Senate in Wisconsin, an intentional personal blow that made headlines across the country,” Nicholson said. “It was deliberate – and it is a true representation of the intolerance of a political philosophy that stands on the false platform of tolerance.”

Each of his parents reportedly gave $2,700 to the Wisconsin Democrat’s campaign in December, the largest amount they can give during the Democratic primary. Nicholson’s brother, Scott Nicholson, also gave the maximum amount allowed, $2,700, to Baldwin last year.