Yes, the field of Republican presidential candidates looks cartoonishly huge. I counted 19 possible candidates back in January. Since then, only Mitt Romney has dropped out, while a few whom I thought were improbable or uninterested are, at least for now, acting as if they are candidates.

No one knows why the field is so big. Just be suspicious of anyone giving an authoritative-sounding answer. Here are the most plausible explanations.

-- Maybe it's to be expected.

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1. It could be a fluke. Numbers of candidates change all the time, and this cycle might have had an random fluctuation.

2. Lots of early candidates never get to the formal announcement stage, and that could still happen this time, especially with the governors: Mike Pence of Indiana (I'm counting him even though he doesn't seem to be running), John Kasich, Bobby Jindal, Chris Christie, Rick Perry and Rick Snyder (maybe you didn't know he was in the running?). Three former governors could also rule themselves out (George Pataki of New York, Bob Ehrlich of Maryland and Jim Gilmore of Virginia). Only a dozen or fewer candidates may end up officially announcing, with further winnowing in the summer and fall.

-- Maybe the incentives were aligned this time.

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3. The Republican landslides in 2010 and 2014 have produced an unusually large number of potential candidates.

4. Marginal candidates are more likely to run when there's no imposing front-runner; Republicans have no obvious heavyweight such as a current or former vice president, or a strong runner-up from a previous cycle.

5. Perhaps Republicans are unusually confident of a November 2016 victory.

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6. The success of long shots Rick Santorum and Newt Gingrich in the 2012 primaries and the earlier surges by Michele Bachmann and Herman Cain in pre-primary polls have encouraged fringe candidates to enter.

7. It's all about the aftermath. Republican politicians and quasi-politicians may believe running will lead to lucrative opportunities of one kind or another after they lose. A cost- benefit analysis is encouraging the candidacies of people who can't win.

-- Or maybe something new -- such as more available money -- is the key.

8. Something in the Republican Party has reduced its ability to winnow the field early - and perhaps later, too. I don't see it myself - but then again I was wrong about candidates dropping out at this point.

9. More money is available, and in larger chunks. Perhaps campaign money is so easy to raise that, as Cook suggests, even weak candidates today can collect enough to run a campaign. There may be enough money to overwhelm the ability of the party to control things. In this case, more candidates than ever could have a chance of winning.

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10. Raising money in larger increments - ideally, from a handful of big donors or even a single mega-donor - makes the grind of raising money less unpleasant, and may tilt the cost- benefit analysis in favor of running.

11. All those millions of dollars sloshing around presidential campaigns may make everything about running more attractive. If the candidates are enjoying first-class accommodations even if thier campaign never catches on, losing will be a lot less painful.

To repeat, we don't know which of these factors, if any, are important. I'd like to know how much time second-tier candidates (and those below that) are spending with potential contributors. And veteran political reporters can tell us whether candidates already on the trail are living higher on the hog than they used to.

The answers matter. Nomination politics defines parties, and parties dominate American politics right now. If something has changed in the process, it could affect how the nation is governed.

Jonathan Bernstein is a Bloomberg View columnist covering U.S. politics.