Every four years, the political world descends on Des Moines for the first nominating contest of the presidential race. And every four years, everyone outside Iowa asks — why? What's so special about Iowa?

Well, nothing really. Its prime placement on the calendar kind of happened by accident. In 1972, the Democratic Party reformed its nominating process to give voters more of a say in the selection of delegates. Iowa, though, had a long and convoluted process for choosing delegates: First they had to hold precinct caucuses, then county conventions, then district conventions, and finally a state convention. The caucuses had to take place in January in order to make the timeline work, which was before any other state held its nominating contest.

At the time, no one thought it mattered which state voted first. But candidates like George McGovern and Jimmy Carter quickly realized the advantages of making a strong first impression, and they rode strong performances in Iowa to the Democratic nomination in 1972 and 1976, respectively. Since then, Iowa has fought to hold onto the power it stumbled onto.

In 2020, technical difficulties, delays in reporting results and errors in the final tallies of the Democratic caucuses turbocharged existing complaints that Iowa did not deserve to go first, especially in light of how demographically unrepresentative it is of the rest of the country. But only Democrats acted on that, reordering their primary calendar so that South Carolina is now the first state to allocate delegates. Republicans kept the same order as always, so here we are.

In a survey last week conducted by Suffolk University, 39 percent of likely Iowa Republican caucusgoers said that "immigration and border security" is the most important issue facing the country today. The next most important issue, the economy, was chosen by 26 percent, followed by "the future of American democracy" at 20 percent. No other issue was chosen by more than 4 percent of voters.

All eyes are on the horse race tonight to see who will emerge victorious from the first-in-the-nation contest for the Republican presidential nomination. Polls have long told us that Trump is a clear favorite — but what issues are motivating Republican caucusgoers in Iowa, and are they in line with their party nationally?

On immigration, Republican caucusgoers in Iowa are far to the right, and seem to agree with some of Trump's stated plans. In an October Selzer & Co./Des Moines Register/NBC News/Mediacom poll, 80 percent of likely caucusgoers said immigration and border security were extremely important to them. A survey from the same pollsters in December found that, when asked about Trump's statement that immigrants who enter the U.S. illegally are "poisoning the blood of America," a plurality of 42 percent of likely caucusgoers said the statement made them more likely to support him. A slim majority, 50 percent, also said they were more likely to vote for Trump when he promised "sweeping raids, giant camps and mass deportations" as an immigration policy. Trump's rivals seem to have taken cues too, as they've embraced more extreme policy rhetoric on immigration and invested in ads focused on the issue.

And on abortion, Republican caucusgoers seem to lie a bit further right than other Republicans. 75 percent want abortion in Iowa to be illegal in all or most cases, per a YouGov/CBS News poll conducted in December>, and half said they wanted the Republican nominee for 2024 to be someone who would support a national abortion ban. These are higher numbers than we've seen in similar national polls of Republican primary voters, and could put some voters off both Trump and Haley, who have been dinged for moderating on the issue during the campaign.

Continued use of ethanol as a gasoline additive is another, more Iowa-specific, issue in the state; as much as half the state's corn crop is used in ethanol production. Per a November ARC Insights/Fields of Freedom survey, overwhelming majorities of Iowa caucusgoers think ethanol is important to both energy independence and the national economy, and want their candidate to include its use in a national energy policy. That means they're likely not fans of the Biden administration's push to expand production and use of electric vehicles — a talking point that most Republican candidates have taken up.

Iowa — along with early-state buddy New Hampshire — has helped shape the results of presidential contests since the dawn of the modern nomination system in the 1970s. The caucuses have provided a pivotal opportunity for candidates to exceed expectations from the start and grab what George H.W. Bush called the "Big Mo" — momentum — after his 1980 Iowa win made him one of the leading Republican candidates that cycle.

The threshold for what could be considered a good or bad performance for each candidate 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. This year, with Trump holding such a large lead, a bigger question than whether he will win is what his percentage looks like and how the rest of the field does in comparison.

Each Republican contender tonight has different goals to meet. For Trump, it's mainly about meeting the expectation of a sizable win — a win with less than an outright majority might look weak for a candidate who is polling north of 50 percent in Iowa. For DeSantis, success appears to be a matter of finishing in front of Haley for second place; otherwise, his campaign may be kaput. Haley, meanwhile, could bring about DeSantis's demise with a solid second-place performance, and set herself up to keep the momentum going into New Hampshire, where she's polling far better. And for Ramaswamy, it's about staying relevant and getting into the double digits.