Let's assume for a moment that Obama wins the Democratic nomination, but goes on to lose to John McCain in the general election. Let us also assume that Hillary Clinton is true to her word and campaigns vigorously and wholeheartedly for Obama ahead of said general election. Finally, let's assume that the rules governing the selection of national convention delegates is not altered in any significant way. Iowa and New Hampshire still get to go first, and the rest of the states inch ever closer to a national primary.
Would the Democratic Party automatically unite behind Clinton on November 5 following an Obama loss the day before (...or for that matter between then and the beginning of the 2012 cycle)? Whether the party does or doesn't is inconsequential because a challenger (or challengers) would emerge regardless. With Iowa set to lead off the process again (given no change in the rules), would Clinton have a problem in 2012? There has been an awful lot of talk about the caucus process during 2008. But because Clinton's performance was less than stellar in caucus states and because she and her surrogates have questioned the level of democracy inherent in them, would she have a problem in the first and most visible caucus? The Hawkeye takes pride in being the first caucus in the nation; a distinction that allows them to go before New Hampshire each cycle.
I don't doubt that Clinton would be more organized in caucus states if she were to run in 2012, but could her stance on caucuses in 2008 give an opponent, say (Sen.?) Mark Warner, an opening in Iowa? As Barack Obama proved, getting off to a good start and proving the viability of your candidacy can be hugely important. Yes, Warner's record and experience speak for themselves and he would potentially be an attractive candidate anyway, but could he (or any challenger) effectively use Clinton's late 2008 caucus position against her? If the economy has rebounded and the Iraq situation has calmed somewhat, then perhaps. But if that is the case, McCain would have a strong case to take to the American electorate and any Democrat (Clinton included) would find it difficult to topple him. If those issues are still the issues of 2012 and if the major Democratic candidates have largely similar methods of dealing with them (sound familiar?), then the caucus quandary could rear its head in Iowa.
The big issue for challengers to overcome would be the idea that 2012 is Clinton's turn. Undoubtedly, that would be a tough mountain to climb. But it looked like a tough mountain to climb in 2008 as well. And then Iowa launched Obama's candidacy. Barring any changes to the rules, though, Iowa will still have the first caucus in 2012.
Rules Matter...but Luck Does Too
The Electoral College Maps (5/21/08)
Colorado Congressional District Caucuses Final Tally: 67% of the Vote, 64% of the Delegates