Someone had to do it. So former San Francisco mayor Willie Brown Jr. stepped up this weekend and kicked off the conversation that has to be had: Should Vice President Joe Biden be replaced on the 2012 presidential ticket?

Brown used the old prediction method: New York governor Andrew Cuomo will become the VP nominee and Biden will land the coveted Secretary of State spot, he conjectured.

There are two problems with that scenario, though: 1.) Cuomo is on the ascent. President Obama is on the decline. No way Cuomo swaps positions. 2.) Biden, God bless him, has been nothing but a headache to Obama as VP. Is the President going to hand loose-lips a higher profile job?

I suspect Brown knows that, but now the subject of musical chairs has been broached. He’s done his job.

This discussion has little to do with Biden’s inveterate gaffes — they are almost charming — nor does it have to do with the brief moments of slumber Biden enjoyed at the President’s deficit speech last week.  It has everything to do, instead, with electoral politics. President Obama’s re-election is anything but assured, and Vice President Biden no longer adds much to the ticket.

In 2008, Biden made sense. Obama was a virtual unknown. He had been an obscure Illinois state senator just two years before, and candidate Clinton was hammering away on the trust issue.  Senator Obama needed a gray-hair standing next to him — one with foreign policy experience who  Americans knew. Biden, a regular on the Sunday talk shows, fit the bill.

But what about now?  What does Biden add today? The President will win Delaware, Biden’s home state, anyway. And whether one agrees or not with President Obama’s foreign policy direction, he is no longer a novice in world affairs.

Where does Biden help?

The argument for keeping Biden is that it shows confidence and stability in the ticket. Replacing him outright would be a risky move, one to make only if deemed necessary. And I suspect that’s what the Obama team, with one eye on the President’s sliding poll numbers, is already quietly discussing. How low do the President’s numbers have to reach to warrant such a dramatic move?

Brown’s prediction this weekend won’t be the last one. The cat’s out of the bag.