And the loser is ...
The winner of the Iowa caucus is very rarely the next president. Looking at the Democratic side, Barack Obama was the only Iowa caucus winner to go on to win the presidency since 1980, when it was actually uncommitted, not Jimmy Carter, that won.
On the other hand, since 1984, five Iowa winners have gone on to lose the presidency.
This year, who loses Iowa matters more than who wins.
Iowa can be relied upon to support the most liberal candidate in the race because the true believers will be in a school assembly hall (or a similar locale) on a Monday evening listening to speeches by their neighbors and moving around the room, which is how you vote.
The problem with Iowa is that the most liberal candidate -- with the exception of the miraculously gifted Barack Obama -- is almost never the one most likely to beat the Republican. If he were, he probably wouldn't win Iowa.
That is certainly true of Bernie Sanders. If he wins Iowa, it means he is the choice of the ideologues. It does not mean he will win the nomination, much less the presidency.
On the other hand, if Elizabeth Warren loses Iowa (meaning she doesn't finish second, maybe not even third), she's in trouble. Candidates from Massachusetts are supposed to win the New Hampshire primary. But it's tough to win New Hampshire if you lose badly in Iowa. We once calculated that even though then-Massachusetts Gov. Michael Dukakis was leading in the New Hampshire polls pre-Iowa, he had to at least finish third or he would lose that lead. He finished first. And Warren isn't running first in New Hampshire.
If Sanders wins in Iowa, it should help Joe Biden, unless Biden loses badly, which should help Michael Bloomberg.
Yes, Bloomberg. Where else will the majority of Democrats who don't think Bernie can win go if Biden gets beaten by Bernie in Iowa and then New Hampshire?