Donald Trump went from defending his controversial remarks to defending his conservative credentials, after his Republican rivals called them into question at Thursday night's debate. 

The billionaire businessman also played down his ties to the Clintons, during and after the debate, as he sought to maintain his status as GOP presidential front-runner and political outsider. 

Speaking with Fox News, Trump confirmed reports Friday that he recently spoke with former President Bill Clinton. But he said "we talked long after I decided to run," quelling speculation that the ex-president might have played some role in his decision. 

"It was really a nothing call," Trump said. 

And as for Hillary Clinton, Trump said, "I will be her worst nightmare and have been." 

More On This...

During the debate, Trump also acknowledged giving money to the Clintons over the years -- but described his giving to many individuals as part of the broken political system. 

He said, in exchange, he demanded Hillary Clinton "be at my wedding," and so she attended. 

Even before the debate, the GOP political punditry was raising questions about Trump's past associations and positions -- as pro-choice, as for a single-payer health care system and other stances. Trump explained Thursday night that he's "evolved" on the abortion issue to become pro-life. 

For Trump, having to defend his conservative credentials is just the latest challenge to his still-surging presidential bid. He seemed to weather controversies over his remarks about Mexican illegal immigrants and Sen. John McCain's war hero reputation, but was repeatedly challenged on other stances Thursday night, at the debate hosted by Fox News and Facebook. 

Trump defended his past support for single-payer health care, saying such a system "works in Canada," but in the U.S., he wants a "private system without the artificial lines around every state." 

Kentucky Sen. Rand Paul shot back, "News flash, the Republican Party's been fighting against a single-payer system." But Trump dismissed him, saying, "I don't think you heard me. You're having a hard time tonight." 

On Friday, though, Trump tried to clarify his response during one of the most memorable moments from the debate stage -- when he refused to commit to supporting the eventual nominee (if it's not him) and rule out an independent run. 

Trump told Fox News on Friday he doesn't want to launch a run outside the Republican Party. 

"I'm leading in all these polls.... And that's what I want to do. I want to run as a Republican," he said. "If I'm treated with respect ... and if I like the person who is going to win if it's not going to be me, I would not run as an independent. But I still don't want to give up the leverage. But I would give it up in that case."