UnitedHealth warns it may exit Obamacare plans

The nation's largest health insurer warned Thursday that it may pull out of the Obamacare exchanges after 2016 – forcing more than a half million  people to find other coverage – after low enrollment and high usage cost the company millions of dollars.

The possible move by UnitedHealth Group raises new questions about the viability ofPresident Obama's signature health law and follows the departure of more than half of the non-profit insurance cooperatives this year. If UnitedHealth drops out, consumers would lose one of the lowest-cost plans available in much of the country, and some wonder how smaller insurers could fill the void.