Hillary Clinton's vow to never again lose the Iowa caucuses, as she did in spectacular fashion in 2008, paid off early Tuesday with a victory by the slimmest of margins.

But for Clinton, that's probably not going to be enough.

Vermont Sen. Bernie Sanders' strong showing almost certainly denies Clinton a glide path to the nomination and prolongs the contest deeper into the calendar than Clinton hoped, by likely giving her opponent an infusion of cash and momentum.

It's also sure to resurrect the questions that have long surrounded Clinton and nagged at Democrats, about why she can't close the deal, why many voters remain cool to her and whether she truly is capable of knocking out a Republican in the fall.

Despite it all, Clinton's campaign was designed to withstand a bad night in Iowa, and a loss in next week's New Hampshire primary, where Sanders leads in the polls. She has the money, the state-by-state organizations and a spate of Clinton-friendly contests coming up that still give her the inside track on the Democratic nomination.

"It's important to take the long view. Unless numbers change dramatically in South Carolina and Nevada and more importantly the states on Super Tuesday, it will be difficult for Senator Sanders to win the nomination," said Mitch Stewart, a Democratic strategist and Clinton supporter who was Obama's Iowa field director in 2008.

David Axelrod, a former adviser to President Obama who directs the Institute of Politics at the University of Chicago, called it "a good night for Bernie."

"The diverse states beyond New Hampshire will be far more challenging for him," Axelrod said. "She's still the favorite, but he will raise big money off of [his Iowa] showing, which could, at a minimum, prolong the race."

Sanders, a Democratic socialist without the youth or biracial appeal of Barack Obama, nevertheless tapped into Obama's voters and this year's angry, anti-establishment wave. His campaign worked hard to organize voters on college campuses.

Sanders said that when he began his campaign in Iowa nine months ago, "we had no money. We had no name recognition and we were taking on the most powerful political organization in the United States of America."

Sanders said Iowans are sending a "profound" message: "It is just too late for establishment politics and establishment economics."

Clinton's campaign came to Iowa knowing it simply could not lose badly a second time here without stoking Democrats' fears that she's too divisive and carries too much baggage to be their best shot at holding the White House.

So Clinton ran against Sanders in all the ways she didn't against Obama in 2008. Then, she waffled on Iowa's importance. This time, she started early and worked hard. Then, she downplayed the history-making nature of her campaign. This time, she was blazing a path for women everywhere. After months of keeping Obama at arm's length, she pulled him close.

After New Hampshire, the race turns more Clinton-friendly, with contests in South Carolina and across the South, where black and Hispanic voters get their say.