With all of its faults, the two major parties over the course of our history have managed to unite common political interests that no third party or independent candidacy has been able to overcome.
"Political parties, for all the nastiness between them, have proved essential to bridge the regional divisions in the United States," the Boston Globe said last week in an editorial critique of a Bloomberg candidacy. "A narrowly focused third party, or an independent campaign, lacks the breadth of shared interests to govern a nation of 300 million people."
Millionaire gadfly Ross Perot blew $60 million on a third-party bid in 1992, but did not win a single electoral vote, and, many believe, helped put Bill Clinton in the White House by drawing votes from the GOP's base.
But what would Bloomberg, a Democrat who ran as a Republican and then became an independent, have to offer apart from his call to end political gridlock in government?
With Hillary Clinton, Obama and John Edwards in the Democratic race, "Bloomberg's pro-science, anti-gun, pro-green, anti-smoking, pro-choice ... just-left-of-center ideology seems a domestic agenda that is already well covered," David Remnick wrote in The New Yorker. "Bloomberg could siphon votes, mainly from the Democrats, but to what end?"
Some election analysts say his chances depend on whether the two parties choose nominees at the fringes that could drive just enough voters to a centrist candidacy selling competence and bipartisanship.
"It would take a stark contrast -- say, John Edwards versus Mike Huckabee -- to give him any room to run. The more likely matchup -- John McCain versus Clinton or Obama -- would put him in the role of a spoiler," said Tom Mann, a veteran presidential-elections analyst at the Brookings Institution.
The spoiler role conjures up a bitter memory for Democrats who well remember Ralph Nader's 2000 run on the Green Party ticket. Nader drew only 2.7 percent of the vote out of more than 105 million popular votes, but he robbed Al Gore of Florida's electoral votes and the White House.
In the meantime, Bloomberg is going over his polling data and waiting to see whom the two parties will choose before assessing his chances. Some say don't rule him out.
"In the Republican red states, a Democrat still gets 40 percent of the vote or more," Zogby told me. "All this guy needs is a plurality of 35 percent in the right number of states, and he could win."