What each candidate needs to do in the Iowa caucuses

In January 1980, George H.W. Bush narrowly won the Iowa caucuses over front-runner Ronald Reagan. Bush had trailed Reagan by 9 percentage points in the final poll of the Republican contest, but he triumphantly beat expectations. Having won, Bush claimed he had the "Big Mo" — momentum — moving forward. And while Bush didn't win the GOP's presidential nod, his Iowa performance put him on course to become Reagan's main rival, and later, the vice presidential nominee.

As the 1980 case demonstrates, Iowa has helped shape the results of presidential contests since the dawn of the modern nomination system in the 1970s. In tandem with New Hampshire's primary, the Iowa caucuses have provided a pivotal opportunity for candidates to exceed expectations from the start, which in turn can boost their fortunes down the line. The threshold for what could be considered a good or bad performance is a moving target influenced by poll numbers, political media and a candidate's own expectations-setting. Beating those marks can raise a candidate's viability in the eyes of the press, donors and voters, precipitating increased and more positive media coverage, stronger fundraising and greater support in later electoral contests.