If Joe Biden decides to run, it will trigger a split between Hillary Clinton and Barack Obama. Neither side will necessarily be looking to split from the other, but the inevitable dynamics of the race will tend in that direction.
Both Clinton and Biden have a tricky path to navigate. Each has to avoid seeming to be the incumbent's third term, thereby incurring all of his negatives, but each must also be true enough to the president's agenda to keep his support and appeals to his followers.
And when two are trying to walk the tightrope at the same time, sharp elbows are bound to come out.
At first, the contest might assume a "he loves me more than he loves you" aspect, but vying for the inside track is sterile and makes for a stagnant and unexciting campaign. It is also a zero-sum game. Only one candidate will be able successfully to position him or herself as the anointed candidate of the Anointed One.
Ultimately, Biden will win the contest. As vice president, he has helped, at every juncture, to formulate the administration's policies. They are his as much as Obama's.
He has to run close to Obama.
And why shouldn't he? While Obama may have his problems with the general electorate with an upside down favorable/unfavorable rating, he is wildly popular among Democratic primary voters. Biden would do well to run in his shadow.
When Clinton realizes she is being elbowed out of the shadow, she has to chart an independent course. She has to "build" on the accomplishments of the Obama/Biden administration, which inevitably leads to having to demonstrate that the programs don't go far enough or haven't worked as well as was hoped.
The more Clinton implies criticism of this thin-skinned president, the more Biden will jump on her comments to widen the breech. He will find a responsive audience in the president's inner circle. Neither Valerie Jarrett nor Michelle Obama are thought to like Hillary Clinton or Bill Clinton very much. They will relay their sensitivity to Clinton's criticism to the boss and widen the split.
The wider it gets, the more it will grow. Clinton will have to articulate sharp differences with the administration other wise she is consigned to being its second best advert, a posture not likely to draw votes.
The polarization over Obama and his policies is the most important outcome of a Biden entry into the race.
And the most inevitable.