Monday night's Iowa caucuses also produced a clear leader among establishment-type Republicans, with Marco Rubio surging into the GOP's top tier. But the Democratic race is clear as mud, with results still trickling in and Hillary Clinton and Bernie Sanders locked in a near tie.
Ted Cruz's organizational strength, his well-funded super PAC and his retail politicking carried the day as the Texas senator bested the billionaire businessman, 28% to 24%, on the strength of evangelical voters.
Monday night's triumph also suggested there are limits to Trump's attacks, too -- showing that voters didn't penalize him for his Canadian birth and his relative lack of friends in Washington, as the real estate mogul had hoped.
But Cruz will find himself on shakier ground as the race shifts to New Hampshire, where Trump has a sizable lead in the polls and establishment candidates such as Rubio are likely to fare better with voters.
For all of Cruz's success in Iowa, the results also underscored the threat posed by Florida Sen. Marco Rubio, another freshman of Cuban heritage, who finished a strong third with 23%.
2. Clinton survives and advances
The winner of Iowa's Democratic caucuses might not be clear until every single one of the state's 1,681 precincts reports.
But for Hillary Clinton, a virtual tie -- in fact, a hairs-width lead, with 95% of precincts reporting -- was enough for her campaign to declare victory.
The former secretary of state will slog overnight to New Hampshire, where victory looks much more difficult to pull off. But Clinton did something important: She blocked a scenario in which Vermont Sen. Bernie Sanders left Iowa with not just a Granite State lead in the polls, but also huge momentum.
Going into the night, if you'd told Democratic strategists that 180,000 people would caucus, they'd have predicted a Sanders victory.
Instead, Clinton staved off a repeat of her disastrous 2008 loss in Iowa. Clinton told supporters she was "breathing a big sigh of relief. Thank you, Iowa!"
Had Sanders defeated Clinton by a clear margin in Iowa, she'd have been facing the prospect of losing both of the first two contests -- setting off major alarms among supporters and donors and risking a total loss of momentum, even as she looks to a firewall of minority support beyond those two states.
Sanders won a huge majority of younger caucus-goers. But Clinton's strong showing among older voters and women were enough to match the enthusiasm of Sanders' youthful supporters.
3. Marco-mentum is real
That cha-ching Marco Rubio is hearing is the Republican establishment reaching for its wallets.
Rubio might have finished third in the real results, but he clearly won the expectations game -- which might matter most of all.
Rubio finished a strong third place with 23% support -- very nearly nipping Trump for second place. He showed he can compete against Cruz for conservatives, and he actually won suburban Republicans, placing first in the population-dense Polk, Story and Dallas counties that are dominated by more moderate, establishment types.
Two good signs for Rubio: He got boosts from late deciders, about 3 in 10 of whom broke in his favor, and from those who value electability, winning 4 in 10 of those voters, according to early entrance polls.
He is also set to pick up the endorsement of South Carolina Sen. Tim Scott, brightening Rubio's outlook in the state that follows New Hampshire.
4. Trump couldn't turn out enough voters
Donald Trump might be the greatest show in politics -- but that didn't translate to a huge new pool of caucus-goers who could push him over the top.
Part of why Trump lost: Evangelical or born-again Christians made up two-thirds of the Republican electorate. Cruz won about one-third of those voters' support, according to entrance polls, while Trump -- despite campaigning with evangelical leader Jerry Falwell Jr. -- and Rubio netted about 20% each.
Cruz spokesman Rick Tyler taunted Trump's campaign, saying of the business mogul's supporters: "They weren't real today, they won't be real next week and they won't be real the week after that."
After stopping by several caucuses during the evening, Trump finished his night by giving a brief, polite speech thanking Iowans and suggesting he one day might buy a farm there even though he didn't win.
5. Woe to the other establishment candidates
Bigger than Rubio's win could be the loss it deals his three rivals for the so-called establishment lane: Jeb Bush, Chris Christie and John Kasich, all governors or former governors.
Rubio got 23%. The other three combined: 7%.
The trio have bet their campaigns on New Hampshire, hoping that the state would not only give them strong finishes but winnow the pack.
That strategy, though, was built in part on the idea that Trump and Cruz would break away from the pack in the Hawkeye State. It didn't account for the strength of Rubio's surge in the race's closing days.
Now, they'll have to contend with the reality that one member of the four-pack has already broken out, giving establishment Republicans still looking for their horse a clear leader. They might have to hope for a Rubio stumble to reshuffle their pecking order.
But Trump also learned two big lessons Monday night: Cruz's strength with the base and his organizational advantages can't be underestimated, and Rubio has turned the race into one with three -- not two -- top-tier candidates.