Ron Brownstein has a piece in National Journal arguing that the struggle for the presidential nomination in both parties could be protracted.
Tomorrow's Michigan primary, however, may determine whether we have another surprise. If McCain wins there and in South Carolina, it's conceivable that he could effectively lock up the Republican nomination on February 5, while the fight between Clinton and Obama goes on into March and beyond. That's just the opposite of what most people were expecting earlier. It seemed like the Democratic race would be decided first.
Which is why Democrats have a lot at stake in Michigan. It would not be a good thing for them if the Republicans were able to begin uniting around a candidate before the Democrats could. The longer and worse the fights are within a party for its nomination, the weaker that nominee tends to be in the general election.