Republican presidential frontrunner Donald Trump stumbled to defend his recent attacks on his top rival’s wife during an interview on a Wisconsin radio station Monday. Trump joined WTMJ’s Charlie Sykes, a prominent conservative talk-radio host in Milwaukee and a supporter of Ted Cruz, to discuss the state of the race. Wisconsin’s primary is on April 5.

Sykes pressed Trump on a retweet the New York businessman published last week that included an unflattering photograph of Heidi Cruz, Cruz’s wife. “Wouldn’t be a good way to start off your Wiscosnin campaign by saying that wives should be off-limits and that you apologize for mocking her looks?” Sykes asked. Trump countered that he was prompted to respond because of a negative online ad against him that featured a provocative photograph of his wife, Melania Trump, who was at the time a supermodel. “He knew totally about that,” Trump said of Cruz. “If he didn’t know about that, it would be a totally different thing.”