Prior to 1972 the Iowa caucuses were not the presidential testing ground they are today. The caucuses moved to the forefront as a result of legislation passed by the General Assembly which dictated the latest date caucuses could be held (the second Monday in May) but did not limit how early they could be held. In addition to this legislation, the Democratic party of Iowa "added a clause to their party constitution requiring thirty days between party functions," (Winebrenner 1987). This resulted in January 24 as the latest possible date for the democratic caucuses in 1972, moving Iowa ahead of the New Hampshire primaries.
Iowa's role in presidential politics is often seen as controversial. The question of why such a small, homogenous state has so much influence is debated every four years. While the caucuses don't always choose a party's nominee, they often add momentum to the front runners and weed out the candidates with weaker showings. The democratic party embraced Iowa as an early testing ground with George McGovern's strong showing in 1972 and Jimmy Carter spending a large amount of time in Iowa to claim an early win in 1976. More recently, Howard Dean's campaign began to fail after a weak showing in the 2004 caucuses and Barack Obama surprised everyone with an early Iowa win in 2008, which many believe gave him the momentum to win the party's nomination and eventually the presidency. Republicans were slower use Iowa as an early testing ground, but George Bush surprised future president Ronald Reagan with a strong showing in 1980, and dark horse candidate Mike Huckabee's win in 2008 substantially extended the life of his campaign.