For the second time this year, there is chatter about President Obama picking a new running mate for his 2012 reelection campaign.

First, it was Secretary of State Hillary Clinton switching roles with Vice President Joe Biden. Now, it’s Obama dumping Biden for the hottest thing on the national political scene, New York Gov. Andrew Cuomo (D).

It’s fun speculation — and the Fix loves political speculation — but it’s completely unfounded at this point.(Cuomo, as would be expected, has already said he won’t replace Biden.)

But where is the chatter coming from — and why?

The reason for the speculation is relatively obvious.

The 68-year-old Biden is the rare vice president that doesn’t appear to be a future presidential candidate himself. (Although he is the second straight veep — following Dick Cheney — to have little future political ambition.) And by keeping him on the ticket, Democrats may be missing an opportunity to groom a future presidential candidate and get ready for 2016.

Cuomo seems like the most likely person to fill that role right now. Extremely ambitious and popular since his days as attorney general, he’s got the makings of a presidential prospect — heck, we’ve already speculated about whether he is the 2016 frontrunner — and broke nationally in a major way by shepherding the state’s new gay marriage law to passage. In theory, Cuomo could help Obama with Democratic base and give the party a fresh face to get excited about.

Though you can make a credible case for the swap, it’s just not going to happen. Here’s why.

First, presidents don’t generally switch running mates unless there is an obvious reason to do so. While the practice happened relatively frequently in the 1800s, only one president in the 1900s – Franklin Roosevelt – switched running mates for his reelection campaign.

Richard Nixon switched vice presidents, but he only installed Gerald Ford as his vice president after his 1972 reelection campaign (Spiro Agnew resigned amid scandal). After Ford became president, he ran for a full term with Bob Dole rather than the man he had chosen to be his vice president, Nelson Rockefeller.

Second, Biden is reasonably popular. Say what you want about the vice president – gaffe-prone, a little loose with the tongue, not always on the same page as the president – the bottom line is: Biden has not proven to be a liability and, particularly in matters of foreign policy, is clearly a trusted adviser.

Biden doesn’t have fantastic poll numbers, but he’s in much better shape than Dick Cheney was. Remember that President George W. Bush, in his memoir, said there was some talk about dumping Cheney for his 2004 reelection bid. If Bush didn’t abandon Cheney then and still won, why would Obama dump Biden now?

Biden was chosen as an agreeable elder statesman that few would object to. And he still fits that mold.

Third, Cuomo could use more time. Democrats say the McCain campaign’s decision to pluck Sarah Palin from obscurity so early in her term as governor of Alaska backfired. So why would they then pick Cuomo, less than two years into his own governorship of one of the biggest states in the union? The vice presidency is a great launching pad, but having just two years under his belt as a governor would not assure Cuomo any kind of frontrunner status in the 2016 Democratic primary.

Fourth, and most importantly, a switcheroo of the vice presidential nominee would reek of panic — of the Obama team looking to shuffle the pieces on the chess board in order to pull off a victory in November 2012.

Given where the race stands at the moment, that would be a considerable overreaction. The state of the economy clearly imperils Obama’s reelection chances, but he’s not in need of throwing the sort of “Hail Mary” pass that swapping vice presidents signals.

Add to all that the fact that people vote for the president, not the running mate, and the swap scenario makes almost no sense.

The Cuomo/Clinton speculation is a fun political parlor game, but there’s no reason to believe there’s anything behind it right now.