Hillary Clinton ended her historic bid for the White House Saturday declaring she would not look back.

"Life is too short ... to dwell on what might have been," she said.

But there are plenty of people who will, since the twisting, unpredictable Democratic primary race will probably stand as a tough lesson to front-runners in campaigns to come.

Perhaps the biggest mistake, aides admit, was she underestimated her rival. But a look back shows the many opportunities lost and missteps taken by both candidates. It also shows the triumphs that kept Clinton in the race through the end, and vaulted Barack Obama over the top.

"She had the campaign wrapped up when she started, everybody said it was hers to lose and yet she lost," said Ted Sorensen, a former adviser to President Kennedy who was supporting Obama. "She thought she was the best but he was better."

The former first lady began the race as the establishment favorite. Bill Clinton was arguably the biggest surrogate a candidate could ask for, and she was pitting her many years in Washington against a freshman senator whose biggest claim to fame was his speech on the floor of the 2004 Democratic National Convention.

But Obama was paving a campaign on a message of change that steadily resonated across the country. Tapping small-dollar donors online, he was able to amass a war chest that soon eclipsed Clinton's. His campaign was ground-up, while hers was top-down.

Clinton first started to struggle at an Oct. 30 debate, where John Edwards and Obama piled on the senator and she seemed to stumble over an answer about a New York plan to offer illegal immigrants driver's licenses.

But the campaign took its definitive pitch downward in the Jan. 3 Iowa caucuses, where Obama placed first, beating Clinton by nearly 10 points. Edwards came in second, in front of the front-runner.

Edwards was not able to trade up his standing in the race after that, but Obama was.

Sen. Ted Kennedy sent a signal to the Democratic establishment that Obama was alright when he endorsed him later in the month, and others followed.

Though Clinton kept her campaign strong with her victory in the New Hampshire primary days later, the victory was still considered a surprise. Pundits were already beginning to predict Clinton doom.

In the ensuing weeks, the gaps in her campaign infrastructure and game plan began to show.

Strategists and Clinton aides say the campaign never tackled the caucus states like they should. Obama had teams rallying supporters in those smaller, activist-driven elections, and they added up in the end. They say Clinton never planned for a race past Super Tuesday, Feb. 5, and spent too much time on the big, blue states like California and New York.

When Super Tuesday and its 22 state contests came, Obama took 13 states to Clinton's nine. Their delegate gain was not far apart, but Obama went on to win 11 straight victories, building a delegate advantage Clinton could not recover from.

In the end, Clinton was left touting her popular vote haul, but it's a delegate game.

"There were so many things that were wrong with the campaign," said Democratic strategist Kirsten Powers. "She didn't really plan well for the whole delegate fight."

Obama's ascent was gradual and strategic. There was no one thing that doomed Clinton. There was no Dean scream. The New York senator was never a passing fancy - she is a political giant with deep Democratic roots, and voting blocs that would not budge.

But there were several moments where it looked like Obama could collapse, or at least be in trouble.

Despite the many whisper campaigns Obama battled - ones that said he was a secret Muslim, that he didn't wear a flag pin because he's not patriotic - his biggest problem was unquestionably his former pastor.

When the anti-American sermons of Rev. Jeremiah Wright Jr. began circulating in mid-March, the biased messages threatened to conflict with Obama's message of hope.

He took heat for not responding definitively and quickly enough, but Obama eventually took Wright to task.

He delivered a landmark speech on race March 18. He did not disavow Wright as an associate, but after Wright continued to promote conspiracy theories -- that the government could be behind AIDS in the black community, namely - Obama broke ties with Wright.

He left his church at the end of May, as the general election began to get underway.

The only real roadblock in his way by the end of May was the dispute over Florida's and Michigan's delegations. Both were stripped after the states held early primaries in violation of party rules. It mounted to a raucous meeting of a Democratic National Committee panel in Washington, D.C. The final decision gave a Clinton a net delegate gain, but it wasn't enough.

Clinton also caused her campaign trouble when she in March told a story about braving sniper fire in Bosnia while she was first lady. Personal accounts from the trip said otherwise, and she had to take back her story.

Also her husband's sometimes-overzealous campaigning, and racially tinged remarks about Obama, seemed to turn some voters off.

Clinton aides may be done with their self-assessment phase. Some blamed former campaign manager Patti Solis Doyle and strategist Mark Penn, both of whom left the campaign, but they did not blame Clinton herself.

Part of the sense in the campaign was that they underestimated Obama's strength, and his appeal, and his sheer fundraising ability.

Clinton stayed alive through 50 state contests by delivering when her back was against the wall. When she had to win, she won. She tried to capitalize on every opening, casting Obama as too inexperienced to handle foreign threats and accusing him of being aloof to the concerns of the working class after he made his infamous comments after rural voters being "bitter."

The doubts she raised about his electability against John McCain in November may persist. But on Saturday she attempted to put them to rest, and she gave him his due for a race well fought.

She called out his "grit" and urged her supporters to set aside differences and unite to take back the White House.

Click here to see a timeline of campaign highlights.  

Click here to read more about the 2008 GOP race.  

FOX News' Aaron Bruns, Judson Berger and Major Garrett contributed to this report.