He acknowledged Tuesday that may have backfired. "I think some people were disappointed that I didn't go into the debate," Trump said in New Hampshire.
Monday showed that 55% of voters who made up their minds in the final days went with Cruz or Rubio, while only 15% of them chose Trump.
Trump and his advisers don't have too much time to figure out what went wrong. With Cruz's win and Marco Rubio's much stronger-than-expected finish Monday night, Trump now urgently confronts the danger of the Florida senator chipping away at his establishment backing in upcoming contests.
The second-place finish should serve as a serious reality check for his campaign, which is in large part based on bucking the traditional rules of campaigning and political engagement. Then again, nothing about Trump is conventional.
"People didn't talk about my second place," Trump said Tuesday night. "They didn't talk about it as positively as they should have."
In the air but not on the ground
There was nothing traditional about Trump's campaign style in Iowa.
From Day One, Trump showed little interest
in retail politics and the intimate settings that have come to define presidential politics in the Hawkeye State. Instead, the billionaire jetted in and out on his private 757, trading in large rallies for town halls, taking a pass on the local delis and diners, and declining to sleep overnight in the state.
The Trump campaign remained tight-lipped about its efforts to get voters out, sharing little to nothing about its grassroots and volunteer efforts on the ground. The campaign swatted away reports of a lackluster ground game, insisting that its supporters in Iowa would turn out in the end because they were so eager to elect a non-traditional candidate like Trump.
It was only in the final stretch that Trump showed minimal interest in retail politics.
He began holding more than one event a day. In January, he made his first stop at a Pizza Ranch -- the famous restaurant chain that is a favorite among presidential candidates. Trump even slept at a Holiday Inn in one of his final weekends in the state.
Meanwhile, Cruz's campaign
had been making inroads in Iowa in the old-fashioned way for months.
The Texas senator crisscrossed the state, ultimately completing the "full Grassley" by visiting all 99 counties in the state. His campaign developed a massive grassroots operation, that according to the campaign 12,000 volunteers fanned out cross the state knocking on doors and making phone calls. It also recruited dozens of pastors and county chairs.
Rubio, in the meantime, came on and surprised everyone at the end. After Thursday's debate, there were rumblings of a Rubio rise, which were tamped down by the Des Moines Register poll released two days before the caucuses that showed the Florida senator in the mid-teens, far ahead of of the others in the establishment lane like Chris Christie and Jeb Bush, but still significantly behind Trump and Cruz.
Rubio finished at 23%.
Hundreds of Rubio volunteers made phone calls to undecided voters in the days leading up to the caucuses, according to campaign aides. During those calls, they found that a good number of Trump supporters -- some frustrated with the businessman's decision to skip last week's Fox debate -- were switching over to Rubio.
Going after Cruz
Trump had an improbable run as the national front-runner for most of the summer and fall. Then, in December, he started to trail Cruz in Iowa for the first time. Up until that point, the two men had refused to attack one another, seeming to believe that voters would find a messy mud-wrestling match distasteful.
But at the first sign of losing ground to Cruz here, Trump swiftly reversed course.
He began to mercilessly attack Cruz
, questioning his ability to serve as president because he was born in Canada. At every opportunity, Trump pointed out Cruz's opposition to ethanol subsidies -- a huge vulnerability for the senator in a state where farming and agriculture are hugely influential.
Trump also jabbed at Cruz's anti-establishment credentials, wondering out loud why the senator had failed to disclose large loans from Goldman Sachs and Citibank for his Senate campaign.
"The truth is, he's a nasty guy," Trump said in an interview on ABC's "This Week." "Nobody likes him. Nobody in Congress likes him. Nobody likes him anywhere once they get to know him."
It did appear that Trump's punches were resonating. At Trump campaign rallies, voters -- including those who had held generally favorable views of Cruz or were undecided -- questioned the senator's authenticity
Cruz, who has tried to stay close to Trump without antagonizing the billionaire, finally hit back, calling his rival a man of "New York values" and blasting his support for eminent domain. Even then, Cruz and his allies seemed much more conflicted about the strategy and wary that it could backfire.
Playing for the evangelicals
Prior to running for president, Trump had a reputation for being many things: a ruthless, litigious businessman; a colorful reality television star; the ultimate Manhattan socialite.
It wasn't exactly the image of a Bible reading, church-going family man.
But on the stump, the GOP frontrunner sought to sand down those rough edges.
He's boasted about the success of his children and his parenting philosophy, including the unbreakable rule in his home of no drugs, alcohol or smoking. Casting himself as a devout Christian
, he has taken the stage at campaign rallies holding a Bible in his hand. When he becomes president, the word "Christmas" would make a comeback, Trump promised.
Two consecutive Sundays before the Iowa caucuses, Trump attended morning church services in the state, even breaking from his usual practice of returning to New York City every night to sleep in his own bed.
All of this has been a part of Trump's months-long and intensifying campaign to win over evangelicals in Iowa -- a sizable and influential constituency with real power to sway the outcome of the caucuses. That outreach became all the more critical when Cruz -- the favorite among Hawkeye State evangelical Christians -- bypassed Trump in the polls for the first time in December.
Trump and his allies were hopeful that two major last-minute endorsements would help swell his popularity within this constituency: Falwell and former Alaska Gov. Sarah Palin
Cleveland Pastor Darrell Scott, a Trump backer who spearheaded an effort to coalesce African-American pastors around the candidate, said it was difficult to overstate the importance of these endorsements.
Palin "brings a lot of evangelical support with her. Then Jerry Falwell Jr. was the icing on the cake," he said.
A religious leader like Falwell in particular, Scott said, was key to convincing undecided voters and on-the-fence churchgoers.
"In Christianity, the sheep tends to follow their shepherd. They will trust the wisdom and trust the decision of their pastor," Scott said. "So when my pastor thinks highly of him to endorse him, there must be something there."
In the end, Cruz still dominated among Iowa evangelicals: according to exit polls
, he won 34% of the evangelical support to Trump's 22%.
The Fox News debacle
Ahead of last week's GOP debate, Trump's long-running feud with Fox News was back in full force.
The billionaire publicly grumbled about debate moderator Megyn Kelly, saying if she couldn't treat him fairly, he may skip the event altogether -- not the first time he had threatened to boycott a debate.
Fox News' response set off a political explosion.
"We learned from a secret back channel that the Ayatollah and Putin both intend to treat Donald Trump unfairly when they meet with him if he becomes president," the network's statement read. "A nefarious source tells us that Trump has his own secret plan to replace the Cabinet with his Twitter followers to see if he should even go to those meetings."
There was no bringing Trump back from this one. He was a no-show.
Instead, less than three miles down the road from the debate, Trump held a rivaling event to benefit wounded veterans. The venue was filled to capacity; political reporters were suddenly split between covering the Trump event and the debate; and the candidate boasted that he had raised nearly $6 million for veterans in a matter of hours.
But while Trump pulled off a political feat in only the way that Trump can, it was clear that the decision rubbed some Iowans the wrong way.
After all, voters in the Hawkeye State take their responsibly of being first seriously, and the debate that Trump skipped was the final -- and critically important -- debate ahead of the caucuses.
Saturday's Des Moines Register poll
showed that 46% of likely caucus-goers didn't care that Trump boycotted the Fox debate, while 29% said they disapproved.
Steve Ziller was one of the 29% that disapproved.
A farmer from Belmond, Ziller was undecided between Trump and Cruz when he attended a Trump rally in Clear Lake on January 9th. Soon after that event, Ziller said he made the decision to support Trump. But that decision quickly got undone when Trump skipped the debate.
"I just think if he's elected president, he's going to have a lot more tougher issues than dealing with a female reporter from Fox," Ziller told CNN the day before the caucuses. "If he would have showed up to the debate and had a good debate, I would have been a 100% for Trump."
On caucus night, Ziller ultimately chose to back Trump. But it wasn't an easy call.
Asked whether the decision was difficult, Ziller responded: "Very."