Party Nomination

A Caucus is a meeting of members of a political party or subgroup to coordinate members' actions, choose group policy, or nominate candidates for various offices. A primary is where the democratic and republican candidates are chosen by states. A Caucus is privately run by parties while primaries are run by the state or national governments. Both Caucuses and primaries are processes that narrow down the ballot on election day so that it makes a majority more likely instead of just a plurality to win.
For most of 2003, Howard Dean had been seen as the inevitable winner of the democratic candidate election. He had been winning in polls and he had very strong fundraising. John Kerry had strong results in the Iowa caucus, however, and this was unexpected. He got 38% of the state's delegates and won in all states except four and the District of Columbia. Kerry and his running mate Edwards won the Democratic National Convention, but lost the presidential election to George Bush.
Kerry's victory in the Iowa caucuses is widely believed to be the way he revived his failing campaign. He went on to win New Hampshire and the February 3, 2004 primary states like Arizona, South Carolina and New Mexico. Kerry then went on to win landslide victories in Nevada and Wisconsin. Kerry thus won the Democratic nomination. Iowa is definitely the way he won, he used a strategy of winning big early. Most other states followed.