Over the years, politicians and journalists develop rules of thumb to describe how these things work. In this cycle, some of those rules seem to be changing.
Start with the old rule that money is everything. When I was working as a political consultant in the 1970s, it was widely assumed that the only feasible way to reach voters and change their minds in most elections was through television ads. And TV ads cost money -- lots of it in big states.
So political reporters anxiously scanned presidential candidates' quarterly campaign finance reports to see which candidates were raising enough money to put ads on the air in crucial primaries. An early start was deemed necessary, because it took time to raise money through candidate fundraisers and direct mail.
Now much of that has changed. In 1992, Jerry Brown kept repeating his campaign's 800 number so people could phone in contributions. In 2008, and especially this time, candidates are raising money through email. That's far faster and cheaper than snail mail.
Money can rush in rapidly. Scott Brown's Massachusetts Senate campaign was taking in $1 million in the last days after polls showed him within striking range. Herman Cain was deluged with millions after the news media reported he had been accused of sexual harassment.
But money doesn't necessarily buy you love. Mitt Romney, who raised and spent lots of money in the 2008 cycle and who can write a personal check for $50 million, has chosen to raise and spend less this time, and he has kept his checkbook in the drawer.
The second way the rules have seemed to change -- let's wait for some results before we say we're sure they have -- is that candidates don't seem to have to do all that much personal campaigning in the early states to win support there.
Romney has spent lots of time in New Hampshire, where he owns a vacation house, and leads in polls. But Jon Huntsman has spent lots of time there, too, and polls only in single digits.
In Iowa, Gov. Terry Branstad has been almost frantic in saying candidates must spend time in the state to win its first-in-the-nation caucuses. The Des Moines Register's candidate tracker proclaims that "Iowa voters expect to see candidates in person, often multiple times, to size up their presidential mettle."