As for Republicans, the number of combinations of plausible results in the early contests rises into the dozens. Mike Huckabee is coming on strong in Iowa, threatening Mitt Romney's lead; John McCain is roughly tied with Rudy Giuliani for second place in New Hampshire; Giuliani and Romney are leading in Michigan; Fred Thompson seems to be narrowly behind Romney and Giuliani in South Carolina. These five candidates all have scenarios of varying plausibility showing them winning the nomination. The key question is whether the winners of Iowa and New Hampshire will get a bounce in the next contests. Bounces have been common, but not universal (Edwards 2004 and George W. Bush 2000 in New Hampshire). Will voters in Michigan and Florida be willing to subcontract their judgment to the voters in Iowa and New Hampshire who have seen more of the candidates? No one knows for sure.
Some Republican insiders are talking about the possibility that none of the candidates gets a majority of delegates. Presumably the nomination will be brokered, probably long before the convention, but not before the party goes through considerable turmoil. I think that's possible; unlikely things can happen (Florida 2000).
What about the general election? Consider two poll results: When the NBC News/Wall Street Journal poll asked voters which party they preferred to win the race for president, Democrats led 49 percent to 36 percent. When the FOX News poll asked which of two specific candidates would do the better job of protecting the country, Rudy Giuliani came out ahead of Hillary Clinton by 50 percent to 36 percent. Those numbers suggest to me that the range of possible outcomes in November 2008 is much wider than it was in November 2004.
What we have not seen yet is a debate between the two parties on ideas. The Democratic candidates have been busy pounding George W. Bush, who will not be on the ballot. The Republican candidates have been busy pounding Hillary Clinton, who may or may not be on the ballot. And candidates in each of the parties have gotten started pounding each other. These arguments are mostly about the past. We haven't heard much yet about the future.