A John Edwards endorsement is one the big X factors left in the race for the Democratic presidential nomination, but several of Edwards' closest advisers from his days on the campaign trail say he's unlikely to throw his weight behind either candidate, according to a report in The Politico.

The article quotes former aides who says Edwards is torn between Hillary Clinton and Barack Obama, and there's a good chance he'll stay on the sidelines.

The speculation comes on the heels of the endorsement Friday of Obama by New Mexico Gov. Bill Richardson, another former candidate for the Democratic nomination.

Richardson was a major score for Obama since both sides were courting him. But Edwards would bring to the table his two presidential campaigns worth of supporters, and the former North Carolina senator's home state has its primary in May.

According to one aide quoted in the Politico article: "He's probably going to remain neutral and sort of try to play on that Al Gore status as party elder."

The advisers interviewed qualified that they're not ruling anything out.

Click here to read the Edwards article in The Politico.