Democrat delegate math
The press is saying (quite rightly) that Ohio and Texas are critical States for Hillary Clinton to win in her quest for the Democratic nomination, and the polls in both of those States presently have her leading by comfortable margins. Not only does Barack Obama have plenty of time to close the gap in both States, he doesn't even need to win those primaries in order to remain competitive or the virtual frontrunner. Because the Democrats award delegates proportionally in virtually every State where they hold nominating contests, there is a formula whereby Obama could still win the Democratic nomination.
Obama has to win the Vermont Primary and Rhode Island Primary on March 4, because Hillary sweeping all four States that day would deal a blow to Obama's campaign from which it would be very difficult to recover. However, assuming Obama can win Vermont and Rhode Island, he may already have won in Hawaii and Wisconsin, both of whom vote this coming Tuesday. If he can pull around 35% of the vote in Texas and Ohio, he will have enough delegates to stay alive. If he wins in Mississippi on March 11, then wins the Nebraska primary on May 13, the Oregon Primary on May 20, and Montana and South Dakota on June 3, all he needs to do is run competative races in Pennsylviania (April 22) West Virginia (May 13), and Kentucky (May 20), and he will likely have won enough delegates to guarantee a brokered convention.
If the Democratic superdelegates are left to decide the nominee instead of the grassroots, it could have a demoralizing effect on Democratic grassroots and depress grassroots motivation in November. Democratic Party brass (including Chairman Howard Dean) are very much aware of that reality and are not likely to let that happen.