June 3, 2008 -- Back when Sen. Hillary Clinton was just starting her campaign, top aides and advisers had a ready answer when asked if she could win the presidency.

"She's already winning," came the response, as repeated by chief strategist Mark Penn, campaign chairman Terry McAuliffe and other top aides and advisers, in memos, press releases and interviews as the campaign began more than a year ago.

It was a rejoinder that fit the "inevitable" candidate — and for a long while, the response fit the facts.

Clinton, D-N.Y., occupied the race's top perch virtually until the voting started, with a campaign that was designed to hover above the opposition and break through with dramatic early victories that would end the campaign cleanly and quickly.

But her campaign, it would turn out, was based on a series of fundamental miscalculations — about the mood of the electorate, the threat posed by Sen. Barack Obama and even the basic rules of the Democratic primary process.

In retrospect, the mistakes started with a faulty assumption: That inevitability itself could underpin the rationale for a presidential candidacy, even in the face of a deep Democratic desire for change and the wide enthusiasm that greeted a first-term senator from Illinois.

When the veneer of invincibility slipped away, so did much of the campaign's strategic foundations, leading to the staff infighting, public eruptions, financial woes and a string of devastating defeats that contributed to Obama's clinching of the Democratic nomination on Tuesday.

Some strategists maintain that Obama, D-Ill., would have beaten any opponent — that he was the man who matched the moment, with a savvy campaign staff that simply played the game better than anyone else.

But here are five mistakes that Democratic strategists and Clinton campaign insiders say contributed to Clinton's downfall — and left Obama as the last candidate standing in the most remarkable primary season in memory:

1. INEVITABILITY AS STRATEGY

Armed with the best brand name in a generation of Democratic politics, Clinton and her aides could afford to be glib early on: She had the wide edge in polls and had the party's top strategists and money folks locked down early — a signal, she hoped, that her candidacy could not be stopped.

Clinton called her campaign a "conversation," yet it was really always more of a machine: The accumulated muscle of the Democratic Party was powering a formidable messaging and fundraising operation on behalf of a skilled, determined candidate — all helping deliver the message that Democrats had better fall in line or get out of the way.

Yet for all the sharp minds that populated Camp Clinton, the campaign failed to account for the broad and deep desire for wholesale change among Democrats; it was, it would turn out, a particularly bad year to run as a de facto incumbent.

"You did not necessarily have a message that was consistent with what people were looking for in a 'change' election," said Chris Lehane, a Democratic strategist who supported Clinton's presidential bid. "It was inherently limiting — and, as the first female presidential candidate, she could have been the candidate of 'change.'"

The campaign struggled constantly with messaging, through a fitful series of attempts to reach different segments of the Democratic Party. She would emphasize her toughness, then her human side.

She seemed to have a lengthy policy prescription for every problem a voter had — meanwhile, Obama fired up arenas filled with thousands of enthusiastic supporters. She seemed to alternative between offense and defense almost by the day, or by the debate.

Clinton would ultimately find an effective voice as a champion of the working class, powering late victories in states including Ohio, Pennsylvania and West Virginia. But by that time, she had lost more ground than she could make up.

2. OLD MONEY, NEW CAMPAIGN

Campaigns need money, and Clinton had the top money men and women in the Democratic Party on board from the start. With former President Bill Clinton literally cashing in chits he accumulated going back to the early 1990s, the Clinton campaign always expected to be able to outspend all comers.

Clinton cornered many of the Democratic "whales," the big party fish who regularly write $2,300 checks and have friends who can do the same. But enough high-profile donors liked what they heard in Obama to ensure at least financial competitiveness — all while Clinton went much of 2007 without engaging Obama directly.

Then something else happened: Obama tapped the power of the Internet like no candidate before. His campaign dove into social-networking sites, not just as a means for supporters to connect but for them to start giving money.

Critically, his donors gave in smaller bursts, meaning they could give again and again throughout the campaign, in increments of $100, $50, or less. Clinton raised far more money in $2,300 bursts — giving her quick cash early, but not a base of donors she could go back to repeatedly.

Both candidates raised slightly more than $100 million in 2007 — shattering all previous records. But then Obama began to pull away: He started out-raising Clinton by more than 2-1 early this year, and regularly brought in more than $1 million a day. The extent of Clinton's money woes was kept away from all but the smallest circle of advisers, costing the campaign valuable time in making up the gap.

Clinton would ultimately be forced to float herself more than $11 million in loans, even while falling further into the red. Her debt to Mark Penn's firm alone has been pegged at $10 million.

The growing financial edge, combined with the elongated nature of the primary season, meant that Obama could compete financially practically everywhere, while Clinton had to make tough spending decisions in critical primaries.

By the end of the campaign, when Clinton regularly mentioned her Web site in speeches it was part of a flagging attempt to create an online donor base that Obama had been harnessing for more than a year.

3. RULES ARE RULES

Terry McAuliffe and top Clinton adviser Harold Ickes know more about the Democrats' delegate selection process than virtually anyone on the planet — but you never would have known that from the Clinton campaign plan.

Clinton aides always said that the race was for convention delegates, yet they never really played it that way.

Nursing a big early lead in superdelegates — party insiders, many of whom felt deep loyalty to the Clintons, who get automatic votes at the convention — the campaign played a traditional early-state strategy that sought to have the campaign wrapped up by Feb. 5.

After a shocking third-place finish in Iowa, Clinton bounced back in New Hampshire. Despite early stumbles, she won the big Super Tuesday battlegrounds of California, New York, New Jersey and Massachusetts. But Obama's dominance in lesser-populated caucus states left the candidates virtually tied on the evening of Feb. 5.

"They underestimated how technically proficient the Obama campaign would be in caucus states," said Jim Jordan, who managed John Kerry's presidential bid early in the 2004 cycle. "Obama had real hard-core enthusiasm — her support may have been bigger, but his was more intense."

The three weeks after Super Tuesday essentially sealed Clinton's fate.

Obama dumped vast organizing resources into states and territories that never appeared likely to play a major role in the nominating process. He reeled off 11 straight convincing victories, from Louisiana and Virginia to Wisconsin and Washington State.

Almost by default, Clinton kept her focus on the next big prizes — Ohio and Texas, which voted March 4. But Obama padded his delegate lead by 121 in the month between Feb. 5 and those contests — a gap that proved impossible to overcome, and that drove news coverage that began depicting Obama — not Clinton — as the inevitable nominee.

Clinton loyalists — including Ickes — also supported the Democratic National Committee's 2007 decision to punish Florida and Michigan for holding too-early contests by stripping the states of their convention delegates.

In the final weeks of the campaign, Clinton focused much of her energy in a last-ditch effort to reverse that decision, though a panel of party insiders would up awarding the two rogue states just half of their original delegate strength.

Yet if Michigan and Florida had counted from the start the race would have looked far different — in delegates, in the popular vote, and in the intangible quality of early momentum.

Instead, Clinton was left vainly arguing that the popular vote should determine the nomination — even though, as her campaign always knew, the nomination is settled by the delegate count.

4. WILD BILL

Early concerns about Bill Clinton's role in the campaign centered on whether he would overshadow his wife. That turned out to be the least of the campaign's problems.

Hillary Clinton would be forced to grapple continually with the mixed political legacy of her husband — on issues of trade and gay rights, for example, where the party's left has long been disappointed in the Clintons. The memories of the scandals of the 1990s were never far off-stage, and her husband's lucrative speaking career and secret donors for the Clinton foundation kept unwelcome questions emerging.

Then there was Bill himself.

An aggressive advocate for his wife, he first hit the trail last summer and was essentially a full-time campaign presence by the height of the political season.

He developed into an effective surrogate for his wife's campaign, particularly in rural areas. But he quickly proved to be a double-edged sword — and the one surrogate who simply could not be controlled by the campaign.

Through a series of angry exchanges with voters and reporters, the bad side of Bill Clinton became evident — in a news environment that had changed drastically in its speed and viciousness in just the eight short years since the Clintons left the White House.

He famously called Obama's contention that he consistently opposed the war in Iraq a "fairy tale," repeatedly served up questionable assertions about his wife and her opponent, and equated Obama's strong showing in South Carolina with that of Jesse Jackson, in comments that drew a harsh backlash that may have cost his wife African-American support in the remaining contests.

A team of longtime Clinton loyalists formed the core of the campaign, with Mark Penn playing the unusual dual role of chief pollster and chief strategist mainly on the strength of his prior relationship with Bill Clinton.

Staff infighting — often with Penn at the center of controversy — left the campaign virtually paralyzed at critical junctures, with major strategic changes coming too late to make a major difference. Patti Solis Doyle left her post as campaign manager in mid-February — contributing to an internal and external sense of campaign turmoil.

Mark Penn was stripped of his formal campaign title in April, after he was revealed to have worked for a trade pact Sen. Clinton opposed. And Bill Clinton, of course, was the one strategist and surrogate who could not be fired, and while he may have brought his wife more votes than he lost, he left the campaign repeatedly off-message.

5. MATTERS OF TRUST

Clinton entered the race needing to overcome years' worth of questions about the Clintons' credibility — in addition to one very big vote in favor of the Iraq war.

While she made great strides in advancing her own reputation — and overcoming liberal skepticism of her campaign — a few slips renewed questions about her candidacy at the worst possible times.

The campaign's trajectory took a sharp turn on Halloween, in Philadelphia, with a straightforward debate question about a plan in New York State to give driver's licenses to undocumented immigrants.

Clinton gave a halting, contradictory response, and her campaign took weeks to put it behind her. It underscored an image of a coldly calculating, excessively cautious politician, and gave Obama, John Edwards and Clinton's other Democratic rivals a much-needed opening to attack Clinton's credibility and honesty.

By the time a better-organized, better-financed Obama delivered a soaring speech at a Democratic Party dinner 10 days after that debate, Clinton's frontrunner status was clearly in jeopardy.

And this spring, just when Obama was facing his campaign's biggest challenge with the emergence of the fiery words of the Rev. Jeremiah Wright, a botched story about sniper fire she supposedly braved in Bosnia called Clinton's credibility into question all over again.

Clinton would close out the primary season surprisingly strong, winning contests long after most pundits had declared the nomination fight over. But Obama was claiming the mantle of inevitability that once was Clinton's — winning by the rules she was supposed to have mastered, in the party she was supposed to have dominated.

Said one Democrat with close ties to the Clintons: "It was just hubris: They couldn't imagine her losing and him winning."