Des Moines: The candidates have already headed to New Hampshire for the next contest in the US presidential nominations race. But Iowa, where they jousted for months, holds key lessons for those seeking the White House.
Here are the most important takeaways from Monday's closely contested vote that saw Donald Trump knocked off his perch, and Hillary Clinton breathe a sigh of relief with a razor-thin win over Bernie Sanders.
Trump: giant with feet of clay
Trump had led in all the opinion polls in the run-up to Monday's caucuses in Iowa, but in the end, he didn't deliver, and conservative Senator Ted Cruz won the night with 27.6 percent of the vote to 24.3 percent for the tycoon. Why?
"While he looked sort of invincible, the reality was that a majority of Republicans did not have a favorable impression of him," David Redlawsk, a professor at Rutgers University who was in Iowa for the caucuses, told AFP.
"The media focus on him went way beyond what the reality was, and voters brought back the reality."
But Cary Covington, a professor of political science at the University of Iowa, cautioned that the large number of evangelical Christians in the state -- a strong base for Cruz -- was always going to be an obstacle for the billionaire businessman.
"Moving forward, he faces a more favorable path," Covington told AFP, with the New Hampshire and South Carolina primaries next up.
Don't forget the ground game
Wooing Iowa voters from afar with crafty advertising, debate stage appeals and showmanship just doesn't work. Perhaps nothing matters more here than a top-rate operation that can get out the vote -- something that Cruz was able to do mightily on his way to victory.
Trump showed he had Iowa support, but he did not engage in the retail politics that is the hallmark of the opening stages of the presidential race. Cruz managed to rally his troops, with an extraordinary multi-pronged push.
Trump's candidacy "befuddled" experts, and poll numbers flew in the face of collective knowledge about the system, noted Joseph Cammarano, an associate professor at Providence College.
"It turns out our knowledge is still relevant: the ground game matters, and a conservative demographic that tends to dominate in Iowa dominated again."
The question now is: will Trump engage more on the ground in the coming weeks?
Wake-up call for Clinton
Sanders showed on Monday that he is a viable alternative to the Clinton machine. While Clinton did not have a bad night -- she avoided the dreaded prospect of reliving her 2008 loss to Barack Obama -- it was not good either, and shows she has work to do to convince the US electorate to choose her.
"Clinton still needs to figure out how to get young people to trust her," Cammarano said.
Sanders, meanwhile, drew huge support from younger voters, and the question is how well the self-described democratic socialist can mobilize the younger generation to come out and vote.
New Hampshire is Sanders's backyard and he is expected to win there. But Clinton has the chance to flip the script after New Hampshire, where the race turns to states like South Carolina where she is more popular.
It then moves to a host of southern states that Clinton may well sweep, Covington said.
Voter anger is real
More than 90 percent of Republicans who participated in Monday's caucuses said they were angry or unsatisfied with the federal government, according to entrance polls. Trump and Cruz tapped into that anger, and it paid off.
"The angry electorate showed up," Covington said. "They were the dominant voices" on the Republican side, he added.
"And Bernie Sanders, in a different direction, taps into that impatience for change on the Democratic side," he said. The Vermont senator earned 84 percent of the vote among caucus participants under the age of 30.
Rubio - consensus candidate?
The rebels won the night in Iowa -- even if Clinton squeezed out a technical win on the Democratic side -- but the Empire can still strike back.
Marco Rubio exceeded expectations with a strong third place showing, proving that a mainstream candidate can still compete in 2016.
Rubio's performance was "very important to the Republican party establishment. They're looking for someone to rally behind," said Covington.
Anger and frustration have marked much of the election cycle, to be sure, but Rubio largely steered clear of the pessimism.
His bounce will give him dramatic increases in media exposure and air time, and donor money could pour in.
Do-or-die time for low-pollers
Thanks for playing. But should low-pollers Rick Santorum or New Jersey Governor Chris Christie really stay in the race? Republican Mike Huckabee and Democrat Martin O'Malley dropped out as Iowa's results were rolling in.
"One wonders what took them so long," said professor Paul Beck of Ohio State University.
"This is going to be a long campaign probably on both sides," he said, and the quicker the Republicans in particular can winnow their field, the better positioned they'll be to take on the Democrats.
Early favorite Jeb Bush's weak performance in Iowa means he needs to up his game immediately, or face irrelevance.
"He's just not performing, so New Hampshire is do or die" for him," Beck said.