Fed up with the partisan system, some Americans are clamoring for a third-party candidate. Among the fresh blood they've sniffed out: New York Mayor Michael Bloomberg.

Bloomberg has recently been urged to run by Gerald Rafshoon and Doug Bailey, two of the founding members of Unity08 , a group formed to overcome bipartisan bickering. But recent events on the campaign trail make a Bloomberg candidacy improbable, if not impossible.

Let's be clear. Bloomberg's financial assets are in place, and he has had a successful political career in New York. He and his cohorts, particularly Kevin Sheekey, who twice helped Bloomberg win races in New York City, know how to be successful. Bloomberg created a personal fortune of $15 billion by some estimates. He spent more than $100 million in two mayoral elections in New York City and won both. He could spend a ton on a presidential bid and not really miss it.

He maintains a Web site that sends email alerts to supporters as if he were campaigning. He has also managed to travel around the country pretty well, and his itinerary includes upcoming trips to California and Texas.

But what political assets does he have going for him in a national race?

This campaign has certainly been about change. Americans don't like where America is headed and want something new. In fact, the Democrats have run heavily on change, and Republicans like Mitt Romney and Mike Huckabee have started to follow suit. Bloomberg is untainted by either party, so he represents the biggest change. Furthermore, he could make the argument that he's the candidate least likely to be bought by lobbyists, given his already staggering wealth.

As a third-party candidate, Bloomberg would not need to gain a majority of the vote to win. Bill Clinton won with about 43% of the vote in the 1992 election and took the Electoral College. Let's assume that Bloomberg could reach the high 30s. That could be enough to win.

Achieving those levels wouldn't be as hard as it seems. Bloomberg merely has to campaign in key states, particularly California, Florida, Illinois, Maryland, Massachusetts, New Jersey, New York and Pennsylvania, that have more independent voters, in addition to many moderates from both the Democratic and Republican parties. The winner-take-all Electoral College favors a candidate taking the middle ground.

It sounds plausible so far. But here come the challenges.

Since Bloomberg needs to score well with moderates, he would need certain candidates to do well. His best matchup would be against John Edwards and either Mike Huckabee or Fred Thompson. Of those three, only Huckabee is a viable candidate.

Barack Obama and Hillary Clinton are the top two Democratic contenders. They both have more moderate policy proposals than John Edwards, who has been much more populist. Obama, in particular, has appealed to many independents. In fact, Unity08 recognizes that its message is getting through and has signaled it may not be able to push for a third-party candidate.

Even if Obama -- with his independent appeal -- doesn't win, Clinton maintains an advantage over Bloomberg. She's a senator from New York. She's very well known on the East Coast, and states like New Jersey, New York and Massachusetts are as blue as they come. Bloomberg needs those votes to have any chance.

On the Republican side, the two front-runners are Mitt Romney and John McCain. Romney has a similar business background to Bloomberg's and also can spend some of his own fortune, estimated at between $250 million and $350 million. Romney has, however, taken a more conservative tack on social issues.

McCain lacks both a fortune and business experience, but he appeals on issues to many of the independent voters that Bloomberg would need. Some like his so-called maverick nature, and other voters find his strong stance on national defense compelling.

Finally, many people don't know who Bloomberg is. According to a recent poll by SurveyUSA , Bloomberg has little recognition. One in four people have no idea who he is. Furthermore, the polls show that he would finish in third place, never scoring more than about 13%, in any of the various iterations tested. (Though spending on advertising certainly could increase those numbers.)

So while the temptation to run must indeed be real, the challenges have built up for Bloomberg. The candidate matchups hurt him more than help, and the polls fail to show any strength. This should be enough to discourage his candidacy.