Donald Trump is already battling low polls in Wisconsin and has suffered further embarrassment when he was criticised by a local radio host for acting like a child by refusing to apologise for insulting Ted Cruz's wife.
Speaking to Charlie Sykes on Wisconsin channel 620 WTMJ, Mr Trump was accused of acting like a “12-year-old schoolboy on the playground” when he mocked Heidi Cruz.
Mr Sykes urged Mr Trump, in a “piece of free advice”, to say to the people of Wisconsin: “Both of us have married beautiful, intelligent women and from now on we are not going to talk about one another’s wives.”
Mr Trump had threatened to “spill the beans” on Heidi Cruz after a pro-Cruz Super Pac posted a risqué picture from GQ of Mr Trump’s wife, Melania, which was taken more than a decade ago, and questioned whether Americans wanted the model to be First Lady.
“I didn’t start it. He started it,” said Mr Trump. “If he hadn’t started it, nothing like this would have ever happened."
“We are not on a playground. We are running for president,” said Mr Sykes.
The interview took place just weeks after researchers discovered that the presidential candidate uses language and grammar that typically correspond to students aged 11 and under.
Mr Trump was forced to listen to a long clip of an advert from an anti-Trump PAC, which listed off his previous insults about women such as Carly Florina and Megyn Kelly.
“I’ve hired tremendous numbers of women,” replied Mr Trump. ”Women are in highest executive positions, I’ve paid women in many cases more then I’ve paid men which is more than most people can say.”
The real estate mogul claimed he helped to break the “glass ceiling” as he gave women “early chances in construction when no one else was doing it”.
Mr Trump added that there should not be a “double standard” when it comes to saying who he is "not a fan of" - this includes Fox news anchor Megyn Kelly and comedian and actress Rosie O’Donnell.
The path to victory in Wisconsin might not be as easy for Mr Trump as in previous states.
A poll from Emerson College Polling Society conducted between 20-22 March forecasted that Mr Cruz has 36 per cent of the vote, a narrow lead over Mr Trump at 35 per cent.
Mr Cruz has a higher lead of 36 per cent over Mr Trump’s 31 per cent, according to a Basswood Research survey conducted for The Washington Free Beacon.
Mr Cruz has also picked up an endorsement from the Republican governor Scott Walker.