I think that if Obama were to win the whole shebang then the Democratic party would definitely she a shift in its constituency whereas a Clinton would essentially keep it the same. I think Obama has the potential to bring in more white collar middle class types which, if you ask me, is a good thing for the Democratic party. One of the Democrats' biggest problems is that their rust belt working class contstituency is shrinking and will continue to shrink in the coming years. There will be no return to the golden days of American manufacturing.
I view it this way; Democrats can go with Hillary Clinton and almost assuredly lose in 2012 by which time shifts in the electoral map will make it nearly impossible for them to win. Or they can go with Obama who has the potential to expand their base and keep them in power after the imminent reapportionment. Still skeptical?
Here's what a Gore+Kerry+Ohio map looks like now:
A 284-254 win for the Democrats. Well that's not so bad until you look at the next map.
Here's what it is likely to look like in 2012 based off most of the 2007 estimate projections:
A 270-268 Democratic win. yikes!
Even though the Democrats still win the 2012 map those projections aren't 100% accurate. Georgia could gain another seat at the expense of Pennsylvania or Michigan. Some projections even have California losing a seat and Florida gaining two instead of one. Where the line falls for the difference between seat number 435 and being number 436 is very much in flux and Democrats can't afford to gamble like that when they're looking forward to 2012. They need to expand their base enough to start winning in Nevada, Colorado, and Virginia in this election and they also need to start looking at Texas, Arizona, and the Carolinas for 2016 or even 2012 if they're lucky.
Bottom line, with current population trends being what they are Democrats need to change their electoral strategy if they want to win elections. They can't keep relying on the current roster of states that Clinton likes to brag so much about winning. They need the Obama states in order to keep winning elections.