A third candidate? Hillary Clinton could do the same and focus on Super Tuesday in the first week of February where New York, New Jersey, and California will be among the big states she will expect to win.
There is also less time this year between Iowa and Super Tuesday - less time for momentum to be built for an Iowa winner or lost for a loser.
The candidates from each of the main parties are likely to be anointed after Super Tuesday or within a month or so of that contest.
Mike Bloomberg could spend $1bn on a campaign and not miss it
So by March it is very likely that a Democrat and a Republican will have emerged.
It is also possible, particularly if large segments of the middle ground in US politics are unhappy (say, with a choice between John Edwards and Mike Huckabee) that the Mayor of New York, Mike Bloomberg, might step in.
Mr Bloomberg does not need to raise any money. He could spend $1bn (£500m) on the campaign and not miss it.
Although he was technically a Republican until recently, his gut sympathies are with the Democrats and he would attract large numbers of centre-left voters.
He is a serious politician (do not think Ross Perot) and he will only stand if he could win.
