The GOP presidential front-runner threw an unexpected curveball into the 2016 campaign this week when he declared that he would boycott the debate sponsored by Fox News amid an escalating feud with the network. He plans to host an event of his own to help wounded veterans.
Suddenly, Trump's rivals will find out what it's like to debate without his bluster and theatrics dominating the stage.
The stakes are highest for Sen. Ted Cruz, Trump's closest rival and threat here in the Hawkeye State. The interaction between the two men, who have spent the last week slinging a flurry of political attacks at one another, were among the most highly anticipated dynamics in the debate as they are battling to finish first in Iowa on Monday.
On the campaign trail Wednesday, Cruz challenged Trump to a one-on-one debate, while mocking his rival for his decision to stay away.
"Apparently, Megyn Kelly is really, really scary," Cruz joked. "Donald is a fragile soul."
Flanking Cruz on stage will be six other top candidates: Marco Rubio, Ben Carson, Jeb Bush, Chris Christie, John Kasich and Rand Paul. Trump's absence in the debate will force each of these candidates to varying degrees to recalibrate their debate night strategies.
READ: What to watch at the GOP debate
Bush has set his sights on a solid performance in New Hampshire on February 9 and has appeared eager to throw punches at the billionaire in the last few debates. He will now be without his favorite antagonist on stage.
"I think it'll hurt him that he's not showing up in the Iowa debate four days before the Iowa caucuses," Bush told CNN's Gloria Borger, calling Trump a master of manipulation. "I just think it can't help him."
Thursday marks a return to the main stage for Paul, who was booted to the undercard earlier this month and decided to skip the event altogether.
Four lower-polling candidates -- Carly Fiorina, Mike Huckabee, Rick Santorum and Jim Gilmore -- participated in a 7 p.m. undercard debate.
Santorum quickly expressed deep frustration with the drama surrounding Trump's decision to skip the debate.
"The entire lead-up to this debate was about whether Donald Trump was going to show up to the next debate," Santorum said. "The people of Iowa ... care a lot about the issues. They care about who's going to be the leader of the free world."
Santorum and Huckabee, two previous winners of the Iowa caucuses, plan to attend Trump's veterans event after the debate.
Gilmore, who has not qualified for most undercard debates, mocked Trump's rival event, as he called himself "the only veteran" running for president this cycle.
"I'm not going to any Donald Trump event over across town on some sort of faux veteran sort of issue," Gilmore said.
He appeared to relish his time in the spotlight, taking issue on several occasions with how many questions he was being asked by the moderators.
"Did you miss me? Did you skip me?" Gilmore blurted out when a question went to Huckabee.
