Democrats in Nevada, Republicans in South Carolina

Tomorrow, Nevada voters will express their presidential preferences in casinos and other places, too. In this confusing caucus state where the rules allow same-day registration, polls show Democrats Clinton, Obama and Edwards in a virtual tie. Also tomorrow is a Republican primary in South Carolina. Steve Kornacki, columnist for the New York Observer, looks at the Nevada race; Michael Scherer of Time magazine says things in South Carolina are getting tough.