On January 3, 2008 all eyes were on Iowa— the first of the Democratic primaries. When the votes were finally tallied, the rest of the nation watched as Barack Obama was declared the winner with 38% support. His campaign hasn’t looked back since.

Information cascades have become synonymous with American primary elections, since voters cannot help being influenced by trends in preceding states. Consider the last two Democratic primaries, which both began in Iowa. In 2004, John Kerry won with 38% and proceeded to clinch the nomination, having captured 46 states. This year Barack Obama’s campaign has been especially competitive since his own win in Iowa. Even those closest to Obama admitted to how crucial the state was in convincing others to jump on the bandwagon. “Iowa– that’s the whole shebang!” Obama’s campaign manager David Plouffe candidly voiced to Michael Crowley of The New Republic. Even Michelle Obama reflected on the reality of the situation: “If Barack doesn’t win Iowa, it’s just a dream.”

This type of cascading, referred to as “Theory of Momentum in Sequential Voting” by Ali and Kartik. While it is difficult to fully comprehend the entirety of their sprawling research document, the team from Stanford and UC San Diego makes an important point about who can be influenced by cascading. Partisan voters will choose to elect their candidate regardless of the circumstance, compared to neutral voters who will cast a ballot based on the current state (i.e. a personal binary signal received). In this way, a lot of the swing voters in the states following Iowa in both the 2004 and 2008 Democratic primaries simply jumped on the bandwagon for a particular candidate. According to Ali and Kartik, these kinds of “history dependent strategies… constitute fully rational behavior” for neutral voters.

Why, then, has Hillary Clinton still managed to be successful despite an Obama cascade? While a cascade is definitely powerful, it can never guarantee a victor. This is because there are always partisan voters who will never change their minds. In addition, neutral voters go through different phases: uninformed and informed voting. The uninformed part, also known as herding, contributes to cascades with subsequent voters blindly casting ballots. The missing piece of the puzzle however, is that voters also have the ability to experience social learning, which can be influenced by signals from the partisan group and especially the media.

While there is still doubt about who will win the Democratic primary, there is little uncertainty that the Obama campaign got a huge boost from an information cascade. Had the results in Iowa not turned out the same, it would likely be a very different race than it is today.