Real estate mogul and potential 2012 presidential contender Donald Trump defended his questioning of President Obama's birth certificate Monday morning with a defiant, "this guy either has a birth certificate or he doesn't."

"I am really concerned," Trump said in a phone interview on "Fox & Friends." "You have no doctors that remember, you have no nurses -- this is the president of the United States -- that remember. ... He could have been born outside of this country. Why can't he produce a birth certificate?"



Trump, who has been flirting with a run for president, first made a remark about the so-called "birther" issue last week on "The View." Obama provided news organizations with a scan of his birth certificate during his 2008 campaign, which some oulets also independently vetted.

"I brought it up just routinely, and now I'm starting to wonder myself whether he was born in this country," Trump said Monday.

Trump also raised the possibility that the rebels in Libya currently receiving backing from the West may have more nefarious allegiances than people realize, advising Obama to address the issue in his speech on Libya Monday night.