I suspect that in the end, this will not be a big deal in the national election. If Clinton gets the nomination, Obama will strongly support her. He knows that if he does not, and the Republican wins, he will be a pariah in the Democratic party. If he wants to be President somewhere down the road, he will need white Democratic voters as badly as Clinton will need black voters this year. Obama is young enough that if he does not get the nomination, he will be doing things with 2016 in mind.