The phase we are currently in might be called the pre-pre-pre-game. Few (if any) of the serious candidates have officially declared they're running, but several have established presidential exploratory committees to pave the way. This phase is likely to last until the summer.
Over the course of the summer, nearly all of the candidates should officially declare that they are running. Some will make official announcements that they have declined to run. Once the participants are finally known, the race will take shape.
The third phase will begin in September, around Labor Day. Late entrants (such as Christie) may announce their candidacy at this time. From this point forward, there will be a high level of energy in the campaign and primary debates will be frequent. During this period, voters in early primary states will be paying close attention to the race.
In January of 2012, with only a month to go before the Iowa Caucus, the primary will take center stage. This is the fourth phase, and it will last until a candidate wins the Republican nomination. Up until this point, few people will have been paying much attention to the race, aside from early primary voters and people very interested in politics.
Back in 2007, none of the candidates understood any of this. They thought the sooner they started campaigning, the better. There was sort of an "arms race," with none of the candidates wanting to fall behind. In reality, their efforts in the winter, spring, and even summer of 2007 were mostly wasted. By campaigning so long before most people were paying attention, they were building sandcastles next to the water: The money and effort they put in seemed to have no lasting impact.
It is easier to see it in hindsight: Rudy Giuliani spent plenty of money throughout 2007 but got nowhere. Mike Huckabee experienced a sudden "boom" in popularity toward the end of 2007, because that was when people were actually starting to pay attention in Iowa. Fred Thompson was criticized for getting into the race later, in the late summer of 2007, but it was his lack of enthusiasm once he was in the race that doomed his campaign.
This time, the candidates understand there is little point in doing too much before the summer. Campaigning is not only exhausting to the candidates; it is expensive (especially if it means terminating a contract with Fox News). When a candidate's campaign is started too early, it often spends money faster than it can raise it, rather than building up assets over time.
Thus, the candidates have collectively made an unstated agreement with each other to hold off beginning the race until later. Most candidates already decideded months (or years) ago that they were going to run, but some are genuinely still making up their minds based on who else is running.
