It all comes down to this. Months of campaigning, attack ads, debates, fundraisers and polls lead to primary season, starting with the Iowa caucus.
So what is a caucus, anyway?
"A caucus — it's a neighborhood meeting," former Des Moines Register political reporter David Yepsen told NPR. "In fact, the term caucus is thought to be a Native American term — an Algonquin term for meeting of tribal leaders."
In Iowa, people don't just show up, flash their license and head to a private voting booth; the process is more communal, ABC News reports. Iowa caucuses are part town meeting, part debate club, and part vote-by-concensus. Iowans meet in libraries, schools, firehouses and other public spaces, and passionate supporters of particular candidates do their best to convince others that they should vote for their candidates.
While Republicans have a secret ballot, Democrats caucus by public head count. If a candidate doesn't get the support of at least 15 percent of the people at a caucus, his or her supporters must choose to support another candidate.
As to the question of why Iowa is first, that's a bit more complicated.
The short answer is that it wasn't planned that way. Iowa first took its place as the first state to select a nominee in 1972, after party leaders decided to space primaries out to increase participation. Iowa has a complex process -- as ABC News explains, the caucuses nominate precinct delegates, who go on to county-wide conventions, then state-wide conventions, and finally to the national convention.
Because Iowa's process is more involved than other states, it had to start early. Thus, a tradition was born.
But political analysts say there are practical reasons why it remains the very first state in the primaries. With 3.1 million people, Iowa has less than half of the population of New York City, making it the 30th-most populous U.S. state. By area, it's the 26th-largest state. Iowa offers the chance for candidates to test the waters in a state that won't break the campaign bank, and well-organized campaigns can send their candidates criss-crossing the state to shake as many hands and knock on as many doors as possible.
If a candidate does well, it can help them build momentum and prompt donors to open their wallets. If a candidate flames out, they can drop out early in the process without competing against members of their own party for donations in populous states where campaigning is expensive.
"Iowa in particular is an inexpensive state to run in, so you can have a candidate who doesn't have billions of dollars, come in and work hard, do some ground, build support and ultimately win," Tim Hagle, a political science professor at the University of Iowa, told Today.com. "That's basically what [Rick] Santorum did [for the 2012 election], when he ran his campaign on a shoe string."
Iowa has had its share of memorable campaign moments, including Howard Dean's infamous "Dean Scream" that was played incessantly by cable news outlets over the next few days, dooming his 2004 bid for the White House, according to Esquire.
Iowa was also where then-Sen. Barack Obama made his first mark, showing the world he was a serious candidate by edging frontrunner Hillary Clinton in 2008, ABC News reports.