Let's take a trip back to Jan. 1, 2011.

Former Arkansas Gov. Mike Huckabee, former Massachusetts Gov. Mitt Romney, former Alaska Gov. Sarah Palin and former House Speaker Newt Gingrich were seen as the most likely Republican challengers to President Barack Obama in 2012. Lesser-known names included Mississippi Gov. Haley Barbour, Indiana Gov. Mitch Daniels and former Minnesota Gov. Tim Pawlenty.

How things change in a year.

Now, with 2011 drawing to a close, only two of those initial candidates -- Gingrich and Romney -- remain in the race, joined by Michele Bachmann, Jon Huntsman, Ron Paul, Rick Perry and Rick Santorum. In between, there was Herman Cain, who spent a month or so in the blinding glare of the front-runner's spotlight before ending 2011 the way he began it: in irrelevance.

Graphs of polling data from the past year show a race more volatile than any in recent memory. Donald Trump had the supposed momentum in April. Then it was Tim Pawlenty. Then Bachmann, then Perry, then Cain, then Gingrich. Now Paul. Tomorrow, Santorum?

None of these people has managed to sustain his or her lead for more than a month or so with an electorate drowning in indecision.

Romney's poll numbers have remained more or less steady in the 20-25 percent range, making him the closest thing Republicans have to a front-runner, but few voters are actively enthusiastic about his candidacy. Some support him because they think he has the best chance to beat Obama next November, even if they aren't enamored with his platform; others are holding their nose because they can't find anyone else they like better. Either way, it is difficult to call him the front-runner when he has had to wait for voters to test-drive every single other candidate in increasing desperation.

Here is a month-by-month look at the highlights and lowlights of the campaign so far. What do you think will happen next?

January - March

Early polls show Huckabee, Romney, Palin and Gingrich, in that order, as the candidates that GOP voters most want to see run, and one poll shows Huckabee tied with Barack Obama at 43 percent in a hypothetical matchup. Of those four candidates, only two -- Gingrich and Romney -- will end up running.

The first three months of 2011 are almost devoid of campaign activity, which is unusual in a party that typically has a front-runner by March of a pre-election year.

When there is activity, its focus is also unusual: While prospective candidates talk about the economy to some extent, they spend a lot more time talking about Sharia law and the threat posed by radical Islam. Huckabee lambasts two Protestant churches for allowing Muslims to worship there when local mosques are overcrowded. Santorum calls Sharia law evil and denies that the Crusades involved Christian aggression, and Cain says flatly that he would not consider appointing a Muslim to his cabinet.

April:

It's all about The Donald -- or so the real estate mogul and one-time Democrat would like voters to believe. Trump jerks voters around for a few weeks with the classic I'm running, I'm running not game and a singular focus on a long-resolved issue: Obama's birth certificate. He flaunts a handful of polls showing him at or near the top of the list of likely candidates, though this may have more to do with his name recognition than his politics.

Former New Mexico Gov. Gary Johnson declares his candidacy on April 21 but is completely overshadowed by the Trump show. However, even that show isn't reaching as many viewers as Trump probably thinks: a Pew Research Center poll shows that 53 percent of Americans cannot name a single GOP contender.

May:

Trump decides not to run for president after all, to the great disappointment of comedians everywhere. He is quick to emphasize, though, that his decision has nothing to do with polls showing that more than half of Americans wouldn't vote for him. My potential candidacy continues to be validated by ranking at the top of the Republican contenders in polls across the country, he insists.

Huckabee decides not to run, either, but this receives far less attention, despite his dominating polls earlier in the year. Governors Chris Christie of New Jersey, Mitch Daniels of Indiana and Haley Barbour of Mississippi also rule out bids.

Four candidates do file official paperwork to enter the race: Newt Gingrich (May 11), Ron Paul (May 13), Herman Cain (May 21) and Tim Pawlenty (May 23).

June - July

Mitt Romney formally declares his candidacy on June 2, followed by Rick Santorum on June 6, Jon Huntsman on June 21 and Michele Bachmann on June 27, bringing the field to eight major candidates. Sarah Palin remains a wild card, stubbornly refusing to confirm or deny that she is considering a campaign, and a movement grows to pull Rick Perry into the race.  

Bachmann, however, is the story of the month, with many Republicans saying she offers a perfect balance between conservatism and electability. She moves quickly into second place in national polls and in Iowa, though she continues to trail Romney. She continues to gain support in July, coming within 8 percentage points of Romney nationally and surpassing him in Iowa. Her base consists largely of Tea Party supporters, a demographic that had previously favored Pawlenty. This poses a serious threat to Pawlenty's status as the strongest conservative challenger to Romney.

August:

Bachmann wins the Ames Iowa Straw Poll on Aug. 13, edging out Ron Paul by just 192 votes and crushing Pawlenty, who withdraws from the race the very next day: the first casualty of a campaign that will only get more volatile in the months to come.

But there is no time for Bachmann to bask in her victory, because something else happens on Aug. 13: Rick Perry enters the race. Within a week, he has rocketed to the top of the polls, building a large lead over Romney and tossing Bachmann casually back into the second tier. Commentators wonder breathlessly whether Perry, who has never lost an election, is unbeatable.

Former New York Gov. George Pataki and U.S. Rep. Paul Ryan of Wisconsin briefly contemplate running for the nomination, but both decide against it.

September:

The GOP debates begin in earnest, and Bachmann promptly discredits her already sinking campaign by asserting, based on what one mother ostensibly told her, that the HPV vaccine can cause mental retardation -- a claim that is roundly panned by medical experts and by her fellow candidates. Perry manages to get through the first half of the month with no gaffes and a still-solid lead in the polls.

But then, at a debate in late September, he defends his support as governor of Texas for making the children of illegal immigrants eligible for in-state tuition -- a position anathema to many conservatives. He might have recovered from that, but he then proceeds to say that anyone who disagrees with him must not have a heart.

This leaves a wide opening for a new anti-Romney front-runner, and Cain pounces, going from single-digit poll numbers to first place in a major straw poll in Florida. Romney retakes the front-runner's spot by default as Perry pops out of the toaster thoroughly burned, but Cain is hot on his heels.

Meanwhile, Chris Christie, who had said in May that he wouldn't run, spends a few weeks teasing the frustrated not-Romney crowd by issuing a series of non-denial denials about reconsidering. Palin decides to join in the fun, too, promising a decision soon.

October:

Christie and Palin finally announce that they will not enter the race, and voters begin, slowly, to resign themselves to the fact that their choices are set.

Cain surpasses Romney to become the latest front-runner, with one poll showing him ahead by a mind-boggling 20 points. He and his supporters ridicule anyone who questions his electability or experience (or lack thereof -- he has never held elected office), along with anyone who dares to say his lead, like Perry's, won't last.

Cain holds on to his lead for the rest of the month, wooing audiences with his catchy 9-9-9 tax reform plan and his brash, tell-it-like-it-is campaign style. But just when you thought he might actually be right about his staying power, Politico publishes a bombshell investigation revealing that at least two women accused him of sexual harassment while he was CEO of the National Restaurant Association in the 1990s.

November:

All of a sudden, Cain is caught in a firestorm over the old sexual harassment allegations. He acknowledges that at least one National Restaurant Association employee received a monetary settlement after accusing him of harassment, while categorically denying any wrongdoing and accusing the media of targeting him because he is a conservative black man.

But the story grows, with a third and fourth woman accusing him of harassment and two of the four women revealing their names, and the fallout accumulates, exacerbated by Cain's fumbling PR efforts. The final straw comes when a fifth woman claims to have had a long-term affair while Cain was married to his wife of 43 years. Once again, Cain denies the allegations, but his poll numbers are dropping precipitously.

He blasts the media for character assassination and vows to stay in the race. Then he says he is reassessing his campaign. Then he vows again to stay in the race. Then he decides not to stay in the race after all -- but he promises his supporters they haven't seen the last of him and announces a Web site through which he intends to influence the remaining candidates.

December:

Cain's promised influence does not materialize, and he and his Web site vanish into oblivion. Meanwhile, Gingrich rockets to the top of the polls, posting double-digit leads nationally and in Iowa, South Carolina and Florida, and cutting into Romney's previously unchallenged advantage in New Hampshire.

After leading the polls for a grand total of 10 days -- approximately a sixth of the combined length of time Perry and Cain led -- Gingrich decides now would be an excellent time to call the election, boasting to ABC News' Jake Tapper, I'm going to be the nominee. It's very hard not to look at the recent polls and think that the odds are very high I'm going to be the nominee.

But then his support takes a nosedive. He falls back into a statistical tie with Romney nationally, and into third, fourth or even fifth place in Iowa -- behind Rick Santorum, of all people. Oops.

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After all this, Tim Pawlenty probably wishes he had stayed in the race.

Sure, he looked dead after the Ames Straw Poll, and in any normal campaign, he would have been. But this has been no ordinary campaign, and who knows -- if he had been as stubborn as Gingrich, he might be sitting in the front-runner's seat as 2011 comes to a close.

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