The griping about Iowa's entrenched pole position in the presidential primary race is almost as old a tradition as the state's first-in-the-nation caucuses themselves. The Hawkeye State is too sparsely populated, too white, too conservative, and too rural to have such an outsized influence on presidential nominations, and it often fails to pick the eventual winner, critics say. Still, for every presidential election since 1972, Iowa has gone first, and with good reason. Here, five arguments why the first-in-the-nation caucuses Iowa will host Tuesday evening are so important to this year's GOP field: 

1. Iowa shows which candidates can "go the distance"...
"One reason the Hawkeye State retains its influence in the nominating fight," says Michael Shear in The New York Times, is that its caucuses require more of voters than just filling in an oval, and more of candidates than just running a few ads. Many Iowa caucusgoers expect to actually meet the candidates. This requires "organizational sophistication" from the campaigns, and "helps separate candidates who can go the distance from those who cannot." Only in Iowa, says Carter Eskew in The Washington Post, "do we get a chance to really follow candidates individually and over many months to get to know and test them."

2. ...And weeds out those that can't
Candidates who don't live up to scrutiny don't make it far past the Iowa caucuses. "Iowa matters because we shrink the field," former Iowa House Speaker Christopher Rants tells CNN. "We weed out those who can't make it." According to the conventional wisdom, "there are three tickets out of Iowa — 'first-class, coach, and standby,'" says Rachel Weiner at The Washington Post. Any candidate who "comes in fourth place or lower will have a hard time recovering."

3. It can catapult worthy candidates to the top tier
Where Iowa "truly gains its importance is in terms of momentum," says Elizabeth Hartfield at ABC News. From Sen. George McGovern's surprisingly strong finish in Iowa in 1972 up to Sen. Barack Obama's decisive win in 2008, candidates who outperform expectations can ride their Iowa finish, and the accompanying "boost of media attention," all the way to their party's presidential nomination. "The Hawkeye State can serve as a catapult for candidacies," says The Washington Post's Eskew, or "a wake-up call to the campaigns of complacent frontrunners" who risk losing everything by losing in Iowa.

4. Iowans give Middle America an important voice
There are plenty of "common-sense and fairly obvious reasons for maintaining Iowa's first-to-vote status," says Jon Lauck in the Claremont Review of Books. Many focus on earnest "Iowans' civic virtues," good judgement, and clean politics. But having Iowa go first "also gives a political voice to the Midwest in campaigns which are often focused on the coasts," especially now that "the coastal media dominates the cultural and political discourse." Since there are no regional primaries, "Iowa serves as a proxy for the wider Midwest and helps to make the presidential selection process more representative of the interests of Middle America."

5. C'mon. Iowa simply shouldn't matter so much
It's absurd that we give a small number of Iowans such "extraordinary power," says Brian Montopoli at CBS News. The 2008 turnout of 120,000 GOP caucusgoers was equal to "4 percent of the population of Iowa, and .04 percent of the total U.S. population." There's just no good reason to give this "overwhelmingly white," ideologically extreme "subset of a subset of a subset" of voters such a determinative role in picking our president. Even worse, says Howard Kurtz at The Daily Beast, Iowa's results are chopped up by the media in a "Cuisinart of spin and obfuscation." To hear the national media tell it, Ron Paul could lose by coming in first, but Romney wins by placing second and Rick Santorum succeeds by taking third place. "Got that?" The Iowa caucuses are "a funhouse mirror, distorting the process as everyone else suspends disbelief and plays along."