Improbable? Yes. But impossible? Maybe not.

So goes the evolving political wisdom about whether a third- party presidential bid by New York Mayor Michael Bloomberg would be viable.

On Tuesday, when the billionaire businessman turned politician announced he was formally leaving the GOP to become an independent, he sent tremors through the nation's political chattering classes.

No third-party presidential candidate has ever won the White House, let alone a former mayor of New York. Yet no other third party candidate has ever had Mr. Bloomberg's unique combination of qualities: $4 billion to $5 billion in the bank, a solid record in high elective office, and a penchant for doing the seemingly impossible.

"At some point in American history – I'll be dead probably – ... we are going to have an independent president," says Larry Sabato, political analyst at the University of Virginia. "The conditions necessary are present for 2008: a very unhappy electorate with neither party producing a candidate who can bring people together. So it's not impossible." But it is improbable, he adds.

And other political analysts agree.

It isn't because Bloomberg doesn't have charisma. The short, divorced, Jewish father of two has proven he has plenty of that, winning fans in working-class Queens and on the upscale Upper East Side .

The CEO turned top city executive has governed with a no-nonsense, nonpartisan, and results-oriented politics. In his statement announcing the severance of his ties with the GOP, Bloomberg made it clear that he'd like to bring his brand of pragmatic politics to a national level.

"Any successful elected executive knows that real results are more important than partisan battles, and that good ideas should take precedence over rigid adherence to any particular political ideology," the statement said. "Working together, there's no limit to what we can do."

But, of course, there are the numbers to consider – in the electoral college. To win, Bloomberg would need 270 votes.

"How does he win 270? I could eat my hat, but I think it's as close to impossible a thing in politics where everything is possible," says Doug Muzzio, political analyst at Baruch College in New York.

So, if it is unlikely that this man who likes to win is setting himself up to lose, could Bloomberg have other motives for leaving the GOP? He insists that he's not planning a presidential announcement.

Some pundits say Bloomberg's real aim in making such a national splash is to keep his political clout in New York. He's technically a lame duck. He'll be out of office in exactly 924 days.

Yet another motive for Bloomberg's decision could be to create a new national platform, Mr. Muzzio and others say.

"Number one, he's articulating a national agenda that in Bloomberg's sense is nonpartisan that bridges ideology and goes for practical results, and he's the spokesman for that agenda," says Muzzio. "The second thing is that he creates an organization to move that agenda, and the third step would be to become the candidate to lead that organization. He's certainly at stage one, and he's done it very consciously."