Trump fires an aide over Facebook posts

Donald Trump fired a political aide Sunday over alleged racist Facebook postings, a sign that the new Republican presidential front-runner is working to add a professional patina to his campaign, as he raised the possibility of a third-party run.

"If I am not treated fairly by the Republican Party I very well might consider that," Trump said Sunday in a phone interview on ABC's This Week.  On the same day, Trump campaign manager Corey Lewandowski announced the firing of Sam Nunberg, an on-again, off-again Trump aide who has been accused of making racist posts on Facebook. Nunberg, who says he doesn't remember writing them, did not respond to efforts to reach him for comment. The posts, which use racial epithets and make mocking references to President Obama's African heritage, were first unearthed by Business Insider.

On ABC, Trump pointedly refused to comply with Republican National Committee chairman Reince Priebus' call for Republican presidential candidates to pledge not to run third-party campaigns if they do not get the nomination.

At the moment, Trump is hopeful he can moot the question: Polls continue to show him leading the race for the Republican presidential nomination. The most recent is a  Wall Street Journal poll, which will be released in full on Monday.

In a preview of the results posted Sunday, the Journal said Trump is the top choice of 19 percent of primary voters, with Scott Walker coming in second place with 15 percent. Trump's poll performance has made him a lock for Thursday's prime-time Republican primary debate, hosted by Fox and Facebook.

In another Sunday appearance on CBS's Face the Nation, Trump opined on the Democratic presidential race, discussing reports that Vice President Biden may be considering a challenge to front-runner Hillary Rodham Clinton.

"I think that Biden would have a good chance at beating her now," Trump said.  "I don't think he could've beaten her six months ago, or even three months ago. I think the e-mail scandal is going to be a devastating blow for Hillary, if you have an honorable prosecutor, which we'll see whether or not that happens, because they're all Democrats." The reference was to Clinton's decision to use a private e-mail account and server when she was secretary of state, which has raised questions about the security of her e-mails and the integrity of the historical archive.

Asked about whether he will release his own tax returns, as a number of other presidential contenders, including Clinton, already have done, Trump took the opportunity to tweak the Democrat again.

"I have no major problem with it," he said. "But I may tie them to a release of Hillary's e-mails."

Trump did not say what percentage of his income he pays in taxes, and was open about the efforts he makes to keep his rates low.