There is definitely chatter going on about Obama dropping Biden as VP candidate in favour of Hillary Clinton.
Here's what I think is behind it.
Israel believes Iran is very close to having a nuclear weapon. Their calculation is to strike now, if they think Obama is going to be reelected, or wait, if they think a new administration might be more favourable to Israel.
The polls now favour Obama.
Therefore, the Israelis are likely to strike at least before January. Indeed, the calculus may suggest striking as soon as they are reasonably certain of an Obama win. That would probably be September or October. Just in time for an “October surprise.”
If they strike, there is likely to be a muscular response from Iran. This will dominate the news for a time; Israeli sources are talking about a month-long war.
Whether or not Obama was a good bet to win before this point, this will probably make him a shoo-in. Nobody can blame him for the carnage, and the natural tendency will be to rally round the Commander in Chief. This also takes the public focus off economics, Obama's weak spot, and puts it on foreign affairs, where he seems to have done a decent job. Or rather, Hillary Clinton seems to have done a decent job.
This development, if it comes, will leave the Republican ticket flat-footed, as its expertise is entirely on domestic economic matters. The Ryan pick cemented that, and struck me as risky in part for this reason.
At this point, Obama doing anything is perhaps a case of spiking the ball, but it does make sense to highlight the foreign policy side by taking on Clinton as VP candidate, giving the Democratic ticket the image of the team who are most likely to be able to handle the foreign crisis. That is not quite so clear with Obama-Biden—Romney and Ryan just might pip them in perceived competence even so. It is Clinton who has been the face of US foreign policy. Presumably, Obama has or soon will have advance warning from the Israelis at least that they are seriously considering an attack.
If he does decide to swap Biden for Clinton, I think it will be an indication that the balloon is going up.
Some say Clinton is unlikely to want the job. However, if she wanted the Secretaryship of State, she might also go for the Vice Presidency in these circumstances. If she wants to succeed Obama as president, then, win or lose, this puts her in a somewhat better position, by eliminating Biden as a rival in 2016. If she does not want to succeed Obama as president, then this is a good way to cap off her political career. Rockefeller made the same decision.