Eighty percent of life is just showing up, as Woody Allen puts it.

Well, not in politics. In politics, showing up is everything. If you don't show up to vote, you do not exist. And in Iowa, we're going to learn whether the Trump voter exists in the numbers suggested by the polls, or whether they are illusory. That's the main thing I want to know from the Iowa caucuses. Is this real, or a nightmare?¹

Armed with that information, we could then make a series of assessments:

If Trump voters do show up in numbers large enough to give him the victory, then they'll likely show up in New Hampshire and Nevada and South Carolina as well, and the obstacles to a Trump nomination shrink considerably. He may very well run the table.

If they show up, but not in numbers large enough to keep Ted Cruz out of the top spot, then the race is still very much up in the air.

If they show up, but Trump, Cruz and Rubio all finish within five or six percentage points of each other,  then Rubio is the winner of the night. Even if he finishes a close third, such a performance would give credence to Rubio's claim that he is the logical standard bearer for the GOP mainstream, a claim that he can then cement in New Hampshire a week later. (If I had to bet -- which I don't -- that's the outcome I'd bet upon.)

Writing in National Journal, the well-respected analyst Charlie Cook puts it this way:

"At this point, my gut sug­gests that by the time we get deep in­to the pro­cess (come March), Trump will ap­pear to have the sup­port of the pop­u­list, less ideo­lo­gic­al third of the GOP, roughly where he is now; Cruz will have con­sol­id­ated con­ser­vat­ives and roughly one third of the party; a con­ven­tion­al can­did­ate (Bush, Christie, Kasich, or Ru­bio) will be pulling about a quarter, with the re­main­ing fifth up in the air. That spells a con­tested con­ven­tion."

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¹On the Democratic side, Bernie Sanders may well win the Iowa caucus, setting him up for a win in New Hampshire as well. But as much as that would excite Sanders' voters, I don't think it would change the basic trajectory of the race. Iowa and New Hampshire are prime Sanders territory. Democrats in those states are overwhelmingly white, and Sanders runs best among white Democrats. The latest CNN poll, for example, gives him 42 percent of white Democrats nationwide, compared to 45 percent for Hillary Clinton.

Among non-white Democrats, Clinton has a 24-point advantage.

See you here later tonight.

UPDATE at 10:05: Well, it looks as though I would have won that bet on the GOP side, with the top three finishers all within a handful of percentage points. The Trump voters did turn out, but at lower levels than the polls predicted, and the night will be remembered as a big win for third-place finisher Rubio.

That may sound odd -- hooray for finishing third!! -- but Rubio now has a real argument that the Bush/Christie/Paul/Fiorina contingent, who together couldn't crack double-digits, ought to fold up the tents and rally behind him. That's the message that he'll take to the funders and the voters in New Hampshire.