Donald Trump is getting slammed from all sides for disparaging comments about Carly Fiorina's appearance, with his GOP rivals once again calling on the Republican presidential front-runner to end the "personal attacks." 

At the same time, Republican candidates are stepping up their own attacks. Louisiana Gov. Bobby Jindal used a National Press Club speech Thursday to ridicule Trump's candidacy, warning the party is in danger of nominating a "non-serious, unstable, substance-free candidate." 

As the criticism mounts over his bid and his behavior, Trump's standing in the polls is holding steady. One recent national poll shows his support topping 30 percent for the first time. 

Yet the Fiorina remarks have put Trump on defense, at least for now. 

Trump made the comments about the former HP exec in a Rolling Stone article. "Look at that face! Would anyone vote for that? Can you imagine that, the face of our next president," Trump told the magazine. "I mean, she's a woman, and I'm not s'posedta say bad things, but really, folks, come on. Are we serious?" 

Asked about his comments on Thursday, Trump told Fox News he probably made them but claimed: "I'm talking about persona, I'm not talking about look." 

He also said he was speaking "in a jocular manner, obviously." 

His GOP rivals weren't buying it. 

Fiorina, who has risen in the polls in recent weeks, suggested in an interview with Fox News' "The Kelly File" Wednesday that Trump was taking notice. 

"Maybe, just maybe, I'm getting under his skin a little bit because I'm climbing in the polls," she said, adding his comments "speak for themselves." 

Former Florida Gov. Jeb Bush also tweeted: 

Wisconsin Gov. Scott Walker tweeted: 

Democratic presidential candidate Hillary Clinton also took a swipe at Trump during a stop in Ohio, saying he "seems to delight in insulting women" and if he emerges, "I would love to debate him." 

Trump has faced criticism before for disparaging remarks about women, and was challenged by Fox News' Megyn Kelly at last month's debate over his rhetoric. 

At the National Press Club on Thursday, Jindal said "silly summer season is over" and Trump should be sent "back to reality TV." 

"We cannot send this narcissist, we cannot nominate this egomaniac," Jindal said. 

The Trump campaign fired back late Thursday, highlighting Jindal's low standing in the polls. "He did not make the debate stage and therefore I have never met him. I only respond to people that register more than 1% in the polls. I never thought he had a chance and I've been proven right," Trump said in a statement. 

While Trump is averaging about 30 percent in recent national polls, according to RealClearPolitics, Jindal's support is under 1 percent.