Finally. More than a year after Donald Trump first announced his 2024 presidential run, six months after Gov. Ron DeSantis of Florida refocused his campaign strategy to be all-in on Iowa, and right in the midst of debilitating winter weather, the Iowa caucuses are upon us. And “The Run-Up” has everything you need to know to understand what might happen today — and what it will mean for the race going forward. What’s at stake is clear: Anyone who is going to slow Mr. Trump on his path to clinching the nomination has to get started in Iowa, with at least a close second-place finish. Going into the caucus, Mr. Trump has a dominant polling lead. But now it’s up to the voters. Iowa voters tend to care more about candidates who can speak more to small-town and religious values. The state’s evangelical leaders have largely backed Mr. DeSantis, but evangelical voters themselves — including people coming out to Trump events in freezing temperatures in the last week — have largely backed Mr. Trump. There are three big questions going into caucus day. One, will people come out and participate despite the weather? Two, are the campaigns organized enough to have made a successful last-minute push, to turn interest into actual votes? And three, will any of it matter, or will the freezing temperatures and snowdrifts mean that no matter the result, campaigns will excuse it away? We’ll know the answers later this week.