It is possible, given his strong momentum and seeming invulnerability to criticism, that Barack Obama can win one or more of the Texas, Ohio, and Pennsylvania primaries, thereby putting an effective end to Hillary Clinton's campaign. But if Clinton wins them all - even narrowly - a different dynamic will enter the Democratic nomination race.
That scenario would mean that neither Obama nor Clinton could possibly amass a convention majority from the "pledged" delegates awarded by state primaries and caucuses: some number of the at-large "super-delegates" will be required to forge the majority of all delegates necessary to be nominated.
Who are the "super-delegates" mentioned? They are the elected officials and National Committee members who are automatically seated as convention delegates. Democrats realized that, after converting most of their nominating process away from state conventions to primaries and caucuses and awarding most of those delegates on a proportionate basis, they had effectively given their nomination to the winner of a national primary - even though it was held on different days. The "super-delegates" were added back to the convention as insurance against a mistake - whether it be a late-breaking scandal or other disqualifying information.
Now, we are hearing that it would be some sort of "offense against democracy" if the "super-delegates" were to vote for anyone other than the popular-vote winner. This is nonsense, of course. The "super-delegates" are only there to do exactly that, where necessary. Otherwise, there would have been no purpose at all to adding them.