Republican presidential frontrunner Donald Trump has re-ignited charges of sexism on Twitter when he retweeted comments calling Fox News journalist Megyn Kelly a "bimbo" for showing off her legs and cleavage on the cover of GQ magazine five years ago.

Trump also uttered the "B" word after he announced that he would not be participating in the GOP debate when Fox refused to dump political commentator Kelly, who Trump insisted was "biased" against him. "I refuse to call Megyn Kelly a bimbo, because that would not be politically correct," he wrote on Twitter. "Instead I will only call her a lightweight reporter!"

In the latest Kelly comment, Trump retweeted a supporter who posted a photo of Kelly's 2010 GQ cover. "This is the bimbo that's asking presidential questions?" the tweet asks.

"The underlying theory behind the tweet seems to be that Kelly has posed for GQ in a black slip and very high red heels so she should now sit silently in a corner. Or, at the very least, she has forfeited her right to ask a presidential candidate questions," writes Janell Ross in the Washington Post. Ironically, notes the newspaper, the candidate's comments re-enforce Kelly's concerns about Trump's attitudes toward women after calling them "fat pigs," and "dogs." Her question about the insults and their potential effects on female voters at the first GOP debate in August 2015 started Trump's feud with Kelly and Fox News.

Trump's retweet was retweeted another 9,000 times. Many comments supported the Kelly dig. "Maybe people call them like they see them!!!!!" wrote one Trump backer.

But many replies to Trump were negative.

"I am mortified that you would retweet this, @RealDonaldTrump," one user wrote. "It is wrong on so many levels."

"[You are] appalling," tweeted another person. "A woman can't be sexy and smart? No to [President] Trump!"

"Not very presidential to refer to a woman as a bimbo sir."

Instead of attending the debate, Trump is holding a fundraiser for veterans at a university in Des Moines, Iowa. But at least one veterans group, the Iraq and Afghanistan Veterans of America, said it would not accept any donations from Trump. The candidate has set up a "Donald Trump for Vets" web site for donations. The money goes to the Donald J Trump Foundation, listed at the bottom of the donation form.