You ask why Obama joined the race to begin with. In my opinion there is a very good possibility that he joined the race for the sole purpose of increasing his name recognition and status in the party. In a year when everyone assumed Hillary would get the nomination (previous to primaries begining obviously) it would have been a safe move for him to be seen on a national platform energizing the party, then gracefully bow out after Hillary winning the first of the primaries. This strategy may have even earned him a vice pres. nod.
However, once primary season began, Obama's campaign took on a new life, and people began seeing him as a possible contender, and as sharing a fresh viewpoint. His campaign then took a new direction. From there it was the American People who have supported him, donated to him and voted for him. His win is honest and earned.
Yes, there has been alot of non-issue noise from both parties that has created ill will. Both Obama and Hillary have said things that should not have been said. Know it is time for the party to galvanize around the nominee selected by the American People and change the disastarous course that W. and the Repub. party has set the USA on.