After Obama's ninth straight win, in another predominantly white state, winning among working-class families, he has an unequivocal lead in delegates that is extremely difficult for Clinton to overcome in the upcoming primaries and caucuses.

Voters in Ohio, Texas, Rhode Island and Vermont -- the March 4 states -- who see a specific policy reason to vote for one candidate or another, will have no reason to switch.

But for the majority of Dem voters who like both candidates, the political reality is this: a vote for Sen. Clinton is a vote for a brokered convention.

And the vast majority of Democrats are terrified of having a brokered convention.