NEW YORK (AP) -- Donald Trump says he is pulling out of a Republican presidential debate he had agreed to moderate in Iowa.

The real estate mogul announced Tuesday that he was stepping back in order to preserve the option of running for president in case he's not satisfied that the eventual Republican nominee can defeat President Barack Obama. The conservative website Newsmax was to host the debate Dec. 27.

But the debate has been in jeopardy ever since Mitt Romney signaled he would not participate. Other candidates bowed out. Only Newt Gingrich and Rick Santorum agreed to take part.

Many Republican strategists warned that a presidential debate moderated by Trump, star of "Celebrity Apprentice," would create a circus-like atmosphere that might diminish the candidates vying to challenge Obama.