Just as it appeared that the Democratic presidential field was finally shrinking to a manageable size, it might just expand again. Former New York Mayor Michael Bloomberg is dropping hints that he will launch his own bid for the White House - and when you're a billionaire, it's the kind of decision that doesn't require a whole lot of outside consulting. So why is he contemplating a run for the highest political job in the land just a few months after announcing he would watch 2020 from the sidelines? Here are a few theories. Because he thinks he can winOk, so this is the obvious response. Bloomberg has plenty of pollsters and political strategists at his disposal and is a very data-driven businessman. It doesn't take an advanced degree in quantitative analysis, however, to realise that the Democratic field, even at this (relatively) late date is still in flux. There are four candidates at or near the top of early state and national primary polls - Joe Biden, Elizabeth Warren, Bernie Sanders and Pete Buttigieg. All of them have their strengths, of course, but all of them also have obvious weaknesses. Biden has failed to turn his high name recognition and ties to still-popular former President Barack Obama into electoral and fund-raising dominance, and he's been nagged with concerns about his age and endurance. Warren and Sanders face questions about whether their progressive policies will play well in a general election, and Sanders has age (and health) issues of his own. Buttigieg is young and has little electoral experience, and has yet to show he can attract the kind of minority voters who make up a large chunk of the Democratic primary electorate. What's more, surveys show there are still plenty of Democratic voters who have yet to settle on a candidate. A New York Times/Siena College poll had "don't know" ahead of all the Democratic choices in four of six presidential battleground states. In a recent Economist/YouGov poll, 22% of respondents said they wished they had "more choices" than the Democrats currently running. After surveying the landscape, Bloomberg could have decided that there was still room for a candidate with virtually limitless resources to join the fray and elbow his way to the top. Because he wants to shape the debate So maybe Bloomberg thinks he can win. But, let's be honest, he faces some long odds. A current New York mayor, Bill De Blasio, has already tried his hand this campaign and spectacularly flamed out. Another self-made businessman, John Delaney, has been campaigning in Iowa virtually nonstop for more than two years with nothing to show for it. Another billionaire, Tom Steyer, has spent gobs of money on advertising and seen enough of a nudge in the polls to land on the debate stage but not much else. Speaking of debates, Bloomberg is not going to qualify for the November one. He may not qualify for any, given the current criteria that requires a minimum number of small donations, and reports are that Bloomberg won't be doing any fund-raising. It takes quite a leap of faith to imagine that Democrats these days are ready to jump over to a New York City plutocrat ex-Republican with a smorgasbord of a record that's business friendly, fiscally conservative and includes opposition to government-run health insurance and legalised marijuana, and support for aggressive policing measures, Assuming Bloomberg acknowledges this reality, perhaps he entered the race not to win but to wrestle a party that he sees drifting dangerous leftward back to the pro-business centre. It may not be a coincidence that Bloomberg's campaign toe-dipping comes at the end of a few weeks where fellow billionaires Bill Gates and Leon Cooperman both expressed concern about candidate Warren's proposed 6% tax on personal wealth over $1bn. Bloomberg may want to enter the race specifically to take down Warren and Sanders, whom he clearly views as too extreme and business-unfriendly to defeat Donald Trump next November or, if one manages to do it, to govern effectively. There's certainly a possibility that a focused Bloomberg campaign with a big advertising budget could be detrimental to the two progressives. It's also conceivable that Bloomberg's entry could help them - by peeling off moderate support from Biden or Buttigieg. The latter seems more likely, given that while Bloomberg may not be able to chip away at Biden's minority support, he seems tailor-made for the kind of educated, affluent white voters who have started to flock to Buttigieg. Another very real possibility, however, is that Bloomberg doesn't get any traction and his campaign, while making some pollsters and campaign advisors a bit wealthier, doesn't accomplish much else.