The only purpose of the Iowa caucuses and the New Hampshire primary — aside from, of course, exposing the nation to the fried pork tenderloin sandwiches in the one and the crisp apple cider in the other — is to winnow the field of presidential contenders to a manageable number. It sure is an efficient process this time. The Iowa caucuses haven’t even begun and the winnowing already is under way.

Not that Sen. Joseph I. Lieberman of Connecticut and retired Gen. Wesley L. Clark of Arkansas are out of contention for the Democratic presidential nomination merely because they decided this week not to campaign in Iowa. But the decisions, made separately for separate reasons, do tell us something, not only about the two men’s candidacies, but also about the two places where the first important state contests occur.

These decisions — and here come the two most mischievous words in journalism and politics — raise questions about both matters.

They make us wonder whether Lieberman, who has spent most of the campaign as the Democrat best known in the field, can truly make a national effort if he won’t compete in a state the Democrats have won in the past four elections — a feat, by the way, that only nine states can claim.

These decisions make us wonder, too, about a political system where contenders for a national office can pick and choose among states and where places like Iowa (2 percent black, 3 percent Hispanic, 1 percent Asian) and New Hampshire (1 percent black, 2 percent Hispanic, 1 percent Asian) have an outsized voice in the politics of an increasingly diverse nation (12 percent black, 13 percent Hispanic, 4 percent Asian).

But these decisions have much more to do with strategy than with geography. Lieberman wasn’t going to win in Iowa, and neither was Clark, and so they are out. Period.

There’s nothing more complicated than that at work here. Lieberman was well-known in Iowa and well-liked, too, but nobody was going to support him in a precinct caucus there, which is a severe disadvantage when you want to be president — and which is why his New Hampshire staff pleaded with campaign officials to pull resources out of Des Moines and pour them into Manchester.

Stark but unavoidable truth: Nothing Lieberman could do would propel him higher than a fourth-place finish in Iowa. George H.W. Bush recovered from a third-place Iowa finish in 1988, but only because the Rev. Pat Robertson was in second. He could, in short, explain away his poor showing. Lieberman would have a lot of explaining to do. Here are some of the candidates who finished fourth in Iowa: John Connolly (1980), Jesse L. Jackson (1988), Uncommitted (1984, behind even George S. McGovern). Not a group an aspiring president wants to join.

Clark wasn’t going to fare much better. He’s a celebrity candidate, not a political candidate, and if there’s one thing the Iowa caucuses — a labor-intensive event requiring the mobilization of tens of thousands of people on a wintry Monday night — aren’t designed for, it’s celebrity, except perhaps for a candidate with a strong identification with the military. The last celebrity candidate to take a shot in Iowa happened to be a military figure, too. He was Sen. John H. Glenn Jr. of Ohio. He finished sixth, behind even Sen. Alan Cranston, in 1984 — and there was a hagiographic movie about him released not long before the caucuses.

It’s no coincidence Iowa behaves that way. You win the state the same way you harvest grain: with patience, perseverance, hard work and a little luck. Clark may have the last element, but not the first three. Former Gov. Howard Dean of Vermont, for gosh sakes, has spent the equivalent of more than seven full weeks in Iowa already. There are only about a dozen weeks left, and for three of them (Thanksgiving, Christmas and New Year’s) most sane people are otherwise occupied. So Clark did what any smart general would do. He ordered a tactical retreat.

Politicians have lost Iowa and won the nomination, of course. Former Gov. Ronald Reagan of California (who lost to George H.W. Bush in 1980) and George H.W. Bush (who in turn lost to Sen. Bob Dole of Kansas in 1988) did it, as did Gov. Michael S. Dukakis of Massachusetts (who lost to Rep. Richard A. Gephardt of Missouri in 1988). Iowa didn’t count in 1992 because of the presence of a favorite-son contender, Sen. Tom Harkin, which meant that almost everyone skipped the state that year. But the most celebrated conscientious objector to Iowa in caucus history, Sen. Albert Gore Jr. of Tennessee, left the state in 1988 to make his stand in New Hampshire (where he finished fifth, with 7 percent of the vote) and the South (where he won only four of 12 contests, one of them Tennessee).

The result of the Gore debacle was an iron law of politics — Don’t Skip Iowa — that has not been broken in contested caucuses — until now.

So what these two candidates are doing is either the desperate thing or the new thing. “They know they won’t do well,” says Arthur Miller, the respected University of Iowa political scientist. “They’re working to keep alive. They’re avoiding embarrassment.”

But there’s one figure in the Democratic drama who can’t do what Clark and Lieberman have done. That’s Gephardt. He comes from a neighboring state. He won the caucuses in 1988. His hopes begin in Iowa. They could end there, too. The departures of Lieberman and Clark clarify the contest for him.

Iowa, the winnower among states, is doing its duty after all, just a little ahead of schedule.

David Shribman is a columnist for the Pittsburgh Post-Gazette.