Donald Trump says he regrets retweeting an unflattering picture of the wife of arch-rival Ted Cruz, in a rare act of contrition from the Republican presidential front runner.

Trump is in pole position to seize the Republican nomination but is doing poorly nationwide among women voters, polls show, and faced stern criticism from all sides in recent days after saying women who have illegal abortions should be “punished”, before he backtracked.

The billionaire property mogul has been engaged in an increasingly personal war of words with Cruz, his nearest challenger in the Republican race for the White House, that even drew in their wives.

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An anti-Trump political group unveiled a controversial campaign ad ahead of votes in Arizona and Utah last month that used a GQ magazine photograph of Trump’s wife Melania lying naked and handcuffed to a briefcase.

Cruz denied being behind the advert, which was accompanied by the words: “Meet Melania Trump, your next first lady”.

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Trump then retweeted a photo compilation of an unflattering photo of Cruz’s wife Heidi next to Melania, a Slovenian-American jewellery designer and former model.