I've tried to come up with some sophisticated, nuanced, theoretically meaningful way to say this but nothing is working, so I'll just say it plainly.
I don't see the Hillary campaign saying a bad word about the voters, even those who vote for her opponents. I don't see the campaign explaining away their losses because of some flaw or failing in the voters. Even the group of Obama voters most vociferous and adamant in their objections to her do not get criticized or condemned. To the contrary, she defended MoveOn from politically motivated attacks. She went to Yearly Kos and spoke without rancor or defensiveness to a deeply hostile group.When she says she is impervious to attacks from the right-wing noise machine, the MSM and political opponents, it shows up in the way she will not be badgered and baited. She can look Richard Scaife in the eye and tell him exactly what she intends to do as President without belligerance and without apology. Their cruelty and crudeness cannot disrupt her calm civility, though she may poke some sly fun at them.
This is not someone who has burned bridges on the Democratic side. In a hard-fought campaign, she has been firm that there will be nothing from her side to prevent resolution and reconciliation within the party. She pulls no punches on issues, but has not stooped to personal attacks of the kind leveled at her by her opponents and even by some party leaders. When somone on her campaign has behaved dishonorably, they are told to leave at once.
Unity is not obedience or falling into line. It is being able to strongly and persuasively present yourself and your objectives and be victorious, but do so in a way that does not demand the humiliation, denegration or destruction of your opponents. It is to treat others as valued colleagues to be won over, not as enemies to be obliterated.
In short, when people speak about the need for party unity, the person who most perfectly embodies this stance is Hillary. These qualities as much as her specific policies, are what make Hillary a compelling candidate for me. No one person, no matter how talented, can achieve the goals of the party. All must be done in concert. All must be done under conditions of cooperation, not coersion.
I do not find any qualities in Obama that indicate he is capable of bringing about this cooperation. I see arrogance, imperiousness, inflexibility, and contempt for those who do not hand him what he wants. He does not appear to want unity, only capitulation.
Hillary Rodham Clinton is the person who is best suited to unify the Democratic Party.