And Marco Rubio has dropped more money on TV than any other candidate, culminating in a 30-minute advertisement he's launching in media markets across the state.
But each of these candidates have something in common: They are bracing for a Donald Trump win in Iowa and planning for the aftermath.
"There will be a lot of momentum swings," Jeff Roe, Cruz's campaign manager, said when asked about the prospects of his candidate losing to Trump here Monday night. "I'm not going to be beholden to what a headline says after any state. That's not the way our campaign is structured."
The comments are striking given how much emphasis Cruz has placed in Iowa. But it's the latest signal that the nominating fight could extend well into spring, despite Cruz warning that Trump could be "unstoppable"
if he were to win here Monday night. Each of the candidates are now trying to position themselves as the Trump alternative, with an implicit recognition that he remains the dominant figure in the race.
"When we announced, we talked about a long process in earning the nomination," Danny Diaz, Bush's campaign manager, said when asked if the former Florida governor could sustain losses in Iowa and New Hampshire.
This all suggests that Trump's decision to skip Thursday night's debate
was hardly the game-changer that many predicted. In fact, it seems to have solidified the current standing in the polls here in Iowa, where Trump is ahead of the pack and rival candidates are positioning themselves for the long haul.
In Iowa, Rubio is gunning for third place, hoping to make the case to voters that he can unite the party behind his candidacy if his rivals who aren't named "Trump" decide to drop out. Bush will spend the night of the Iowa caucuses in another state: New Hampshire, a sign of where his focus is.
And Cruz has shifted his final round of ad buys
to target one man -- Rubio -- a signal that the Texas senator wants to maintain his position in second place rather than knock off Trump.
Speaking to reporters here in this town nestled next to the Mississippi River, Rubio said his campaign would have the resources to last beyond the first four primary states, even if he didn't win there. And unlike Cruz, who boasted a fundraising haul of $19 million
in his bank account, Rubio will have far less -- something he said wouldn't affect his ability to stay in the race beyond March, even if Trump wins big in Iowa and New Hampshire.
But as he's done for weeks, Rubio didn't take aim at Trump, instead focusing on Cruz, hoping that a Cruz loss here in Iowa will be a momentum-killer from which the Texas Republican won't be able to recover. Eventually, Rubio hopes, he'll be able to place higher than the rest of the non-Trump candidates, turning the battle into a two-man race between him and Trump.
Cruz, Rubio said, was "worried about my candidacy."
"I think people are starting to learn the truth about Ted on immigration and a bunch of other issues that show a history of calculation -- and that's starting to hurt him," Rubio told reporters here in Eastern Iowa, warning that Cruz wouldn't be able to beat Democratic front-runner Hillary Clinton.
Courting social conservatives
Despite the growing expectation in the field that Trump will win Monday night, the campaigns continued to aggressively court voters here in the final days, hoping to woo late-deciders -- particularly evangelical Christians, who will play a big role in Iowa.
Speaking to supporters here, Rubio, a Roman Catholic, touted his anti-abortion views and his religious faith. And asked by reporters about his abortion views, Rubio maintained a hard line, saying the only exception on abortion he backs is to save the life of a mother -- not if a pregnancy is caused by rape or incest. While he'd sign a bill to ban abortions that had multiple exceptions, he signaled that he'd only insist on one exception -- "if a mother's life is in danger."
"We'd have to have that," Rubio said, a position bound to give Democrats ammunition.
On Saturday, Rubio heads to northwest Iowa -- the most conservative part of the state where Cruz and Trump are poised to do well.
But bracing for Rubio's surge, Cruz's campaign is already trying to draw a wedge between him and social conservatives there -- even more so than their focus on Trump.
Rep. Steve King, who represents that district and is co-chairman of Cruz's campaign, said that Rubio's views on the Supreme Court's decision to legalize same-sex marriage would hurt him there.
"It was Cruz who said this decision will not stand," King said. "It was Rubio who said this was the law of the land."
Looking past Iowa
As Trump is seemingly ignored in Iowa, the candidates are increasingly focusing on New Hampshire and beyond. Rubio is spending money on the fourth primary state -- Nevada -- to try to pull off a victory there if he falls short in the first three.
And candidates who have not spent as much time in Iowa, like New Jersey Gov. Chris Christie and Ohio Gov. John Kasich, are putting an enormous focus on New Hampshire.
In a sign that they are vying to be the alternative to Trump, Kasich and Christie have increasingly focused on each other, while Christie has taken increased aim at Rubio. Rubio, on the other hand, has increasingly ignored Christie as the New Jersey governor has fallen in the polls.
Mike DuHaime, Christie's top adviser, said his campaign was built to last beyond New Hampshire, even if his candidate ends up in fourth place or lower. He predicted late-breaking voters would move his candidate's way -- and eventually more money would fill his coffers.
"This is going to be a four, five-person race," DuHaime said. After that, DuHaime said, "The money will start to come in."