Perry and Cain
The Republican primary field was shaken up in August 2011 by Rick Perry's much-vaunted entry into the race. Trumpeted by red-blooded conservatives as the real deal, the Texas governor turned out not to be ready for primetime.
Revelations in October about his family's "Niggerhead" hunting camp were followed by a bizarre speech in New Hampshire that led commentators to suggest he was drunk or on drugs.
Perry went on to display a tenuous grasp of policy. In his most embarrassing moment, he struggled during a live debate to remember the third government agency he wanted to eliminate.
Fumbling for an agonizing 45 seconds, he finally gave up, concluding apologetically: "The third one, I can't, oops."
If Perry was the great disappointment, the big surprise was Herman Cain.
Hard to believe now, but the black Tea Party activist from Georgia led opinion polls for almost a month before his campaign was torpedoed by a string of sexual harassment allegations in late October.
The former CEO of Godfather's Pizza peppered lively interviews and debate performances with numerous mentions of his wildly simple 9-9-9 tax plan.
Asked in a TV interview if he was ready to avoid gaffes, Cain famously replied: "I'm ready for all the gotcha questions and they are already starting to come. And when they ask me who is the president of Ubeki-beki-beki-beki-stan-stan, I'm going to say 'you know, I don't know.'"
Two Cadillacs and Romney'S $10,000 bet
During the primaries, Romney, who was born into privilege and earned an estimated $250 million fortune at Bain Capital, provided plenty of ammunition to critics keen to paint him as out-of-touch with the average voter.
In a December debate with Perry, who routinely managed to get under his skin, Romney offered the Texas governor a $10,000 bet during an argument over health care. $1 would have sufficed.
Romney came unstuck again in February while trying to woo voters in his native Michigan, telling a crowd that his wife Ann "drives a couple of Cadillacs."
The Obama campaign used these and other gaffes such as: "I have some great friends who are NASCAR team owners," "Corporations are people, my friend," and "I like being able to fire people," in later attack ads.
Romney, Gingrich or Santorum?
Different candidates won the first three Republican voting contests: former senator Rick Santorum took Iowa, Romney triumphed in New Hampshire, and former House speaker Newt Gingrich pulled off a shock victory in South Carolina.
Gingrich turned the tables brilliantly on CNN host John King for opening the pre-vote debate in South Carolina with a personal question about his ex-wife, receiving a standing ovation from the audience.
"The destructive, vicious, negative nature of much of the news media makes it harder to govern this country, harder to attract decent people to run for public office, and I am appalled that you would begin a presidential debate on a topic like that," he scolded.
Santorum later emerged as the greater threat, but Romney, who had always given off the air of the inevitable nominee, built up an unassailable lead.
Santorum suspended his campaign after losing Wisconsin in April and weeks later Romney was declared the presumptive nominee.
Obama's "you didn't build that"
Obama made a major gaffe on July 13 during a campaign speech in Virginia when he said "You didn't build that" when trying to explain that successful businesses rely on public infrastructure.
Conservatives seized on it as an insulting defense of "Big Government" and used it remorselessly in later attack ads.
Ryan gets the nod
Several names were bandied about as Romney's potential running mate and his decision to plump for the relatively young chairman of the House budget committee, Paul Ryan, took some commentators by surprise.
But Ryan, 42, and his picture-perfect family wowed the August convention. The attachment to the ticket of a man seen as an intellectual leader in the Republican Party added policy depth and energized the conservative base.
Ryan did contribute one pearler of a gaffe, however, boasting to a conservative radio host of his "two hour and 50-something" marathon time. Liberals were delighted to discover his real time was over four hours.
Bill Clinton's bravura convention turn
Obama enjoyed a slender lead in the polls going into the Democratic convention in early September.
His speech was well received. First Lady Michelle Obama's went down even better. But the star turn came from an old master: Bill Clinton.
The last two-term Democratic president took on the role of "explainer-in-chief."
For days Obama aides had been pinned on the back foot by a simple question repeated ad nauseam by the Romney campaign: "Are you better off than you were four years ago?"
Clinton set about dismantling the Republican argument piece by piece, telling American voters no president could have turned around the mess Obama inherited in just four years.
"Conditions are improving and if you'll renew the president's contract you will feel it. I believe that with all my heart," he implored.
Polls after the convention showed Obama opening up a clear lead, with Clinton getting a lot of the credit.
Romney's "47%" remark
Obama's post-convention bounce was boosted by the most significant Romney gaffe of the campaign. It came via a secretly-recorded video from a May fundraiser and the content was political dynamite.
In the tape, released on September 17, Romney was heard telling an elite crowd that 47% of the country would vote for Obama no matter what. He said these people were "dependent upon government... believe that they are victims... believe the government has a responsibility to care for them."
"My job is is not to worry about those people. I'll never convince them they should take personal responsibility and care for their lives," he concluded.
In trying to make a point about people who pay no income tax, Romney had written off almost half the electorate. He later sought absolution, admitting that his comments had been "completely wrong," but the damage was done.
Obama had the momentum coming out of the Democratic convention, but Romney, whose campaign had promised "zingers" galore, stole it back at the first presidential debate on October 3 in Denver, Colorado.
Where Obama appeared irritated, Romney was calm and collected. While the president was hesitant and stumbling, his challenger was aggressive, clear and engaged.
Romney took some heat for suggesting he would fire Big Bird -- by cutting funding to public broadcasters such as PBS -- but his strong showing combined with Obama's no-show catapulted the Republican into the lead in national polls.
Vice President Joe Biden righted the Obama ship a little during his one-off encounter with Ryan in Danville, Kentucky.
He set about Romney's running mate with relish, appearing incredulous at many of his statements and punctuating his replies with astonished exclamations like "Amazing!" "Incredible!" and "Malarkey!"
There was huge anticipation leading up to the second presidential debate on October 16 and the prayers of Obama supporters were answered as he came out firing on all cylinders.
Romney's assured overall performance was overshadowed by his response to a question about equal pay when he used the ill-conceived phrase "binders full of women" to refer to the resumes he was given while governor of Massachusetts.
The final presidential debate on October 22 did nothing to budge the election needle, which was still moving steadily in Romney's direction.
Obama did have one memorable smack-down. When Romney suggested the US Navy was smaller than at any time since 1917, the president suggested his opponent didn't understand the modern military, adding: "We also have fewer horses and bayonets."
The October surprise
US presidential campaign watchers often talk of the October surprise: the unexpected event that can upend a race.
This year it came in the form of the largest Atlantic storm on record, Hurricane Sandy, which came crashing into the United States on October 29.
Campaigning was put on hold as the superstorm laid waste to entire communities in New Jersey and New York, claiming more than 110 US lives, shutting down the stock exchange and leaving millions without power, including all of lower Manhattan.
The effect on the race was hard to quantify, but it gave Obama the opportunity to display his leadership skills in a time of crisis.
The Romney campaign, on the other hand, had no choice but to put its fiercest attacks on hold and show solidarity.
Opinion polls in the aftermath of the disaster showed Obama blunting Romney's momentum if not regaining some of his own and the president retained a slim advantage in the decisive swing states going into election day.