It's the Super Bowl of politics for Iowa and new rules for the caucuses could have a dramatic impact on the outcome with there now being three possible ways for the candidates to spin the results.
Sen. Elizabeth Warren's event at Simpson College drew a large crowd Sunday, filling the hallway outside the auditorium. But Warren didn't miss an opportunity to make the connection.
"I've been in Washington for the last week and we're trying to get around to as much of Iowa as possible," she said.
Jim Murray and his 17-year-old son Casey from Lake Bluff, Illinois were in the overflow crowd. Casey will get to vote for the first time next month.
"I am here just to see as many of the candidates as I possibly can so I can make an informed decision," Casey Murray said.
Jim Murray said, "I'm kind of a moderate Republican who doesn't really feel like I have an option on that side of the aisle this year so, trying to get educated about options."
Many voters are still unsure about who to support come Monday.
"I'm not sure I'll know until I walk in who is my one, and who my two is," said Des Moines resident Jenny McCoy.
Des Moines resident Makenzy Jean is also still mulling over the decision.
"I do plan on caucusing tomorrow and I am still deliberating over two candidates," Jean said.
The caucuses start Monday at 7 p.m. For the first time this year, they'll report the first and second round votes as well as state delegate totals, meaning several candidates could claim victories.
"I think it's entirely possible that candidates will work very hard to craft a narrative about how their performance, using anyone of those three sets of numbers, position them really well," said Rachel Paine Caufield, a political science professor at Drake University.
The highly anticipated poll from the Des Moines Register and CNN was cancelled at the last minute after one of the survey's respondents raised concerns about the integrity of the poll.
Three of the candidates, Senators Bernie Sanders, Elizabeth Warren and Amy Klobuchar, are heading back to Washington Sunday night due to the impeachment trial, so they won't be in Iowa to campaign on the final day.