THIS EVENING the people of Iowa -- well, about one in 10 of them anyway -- will journey through the snows to participate in caucuses. In so doing they will inaugurate -- that is, if you forget the incessant campaigning of the past few months -- the presidential nomination process. Their act of participatory citizenship will keep alive a venerable rite that stretches back to the early history of our politics -- back to, oh, 1976, when Jimmy Carter built the Iowa vote into the first important contest of the electoral calendar.

In the lead-up to the vote, the candidates all have said that they don't expect to do well, and some even insist that they don't particularly mind anyway. On the Republican side, John McCain has given Iowa a pass, preferring to concentrate his limited cash on campaigning in New Hampshire and South Carolina. On the Democratic side, Bill Bradley has been complaining that the caucuses serve entrenched interests and should not be taken seriously. The Bradley protests should not be taken seriously, either: The candidate has spent $1.6 million wooing Iowa's voters with television commercials.

After the vote, a miracle will occur: Most candidates will declare themselves delighted with their victories. Because each was honestly expecting a mere smattering of votes, you see, each will receive more than expected; and in caucuses you don't actually have to win in order to win -- you merely must exceed expectations. Sometimes you can even lose by winning, if you get more votes than everybody else but fewer than was anticipated.

Anticipated by whom? It is rude of you to ask, and explaining would be tedious. But we can say that the anticipators-in-chief agree that, in today's Democratic contest, Mr. Gore needs to beat Mr. Bradley by at least 10 percentage points in order to win. Anything less and Mr. Bradley will be deemed to have "momentum," a sort of magical halo.

On the Republican side it is less obvious how large a margin Mr. Bush needs, because he faces five opponents. This murkiness may shift attention to other candidates. Mr. Forbes needs to come in a convincing second in order to look strong; if he comes third or worse, he may be the exceptional candidate (like Sen. Phil Gramm in 1996) who concedes defeat in Iowa and withdraws from the primaries. But the intriguing man to watch is Mr. McCain. By refusing to set foot in Iowa, Mr. McCain has kept the expectations barrier flat down on the floor -- allowing him to vault it easily and so perhaps claim victory.

And how to identify the winner? There's no point asking how many convention delegates each man got. Just check whose picture appears on the covers of the news magazines.