No matter the nominee, the Democratic Party should win the White House in 2008. Let's call it the "Perot Effect" similar to '92 and a flashback to Wallace in '68.
The defining issue is Stem Cells. But it includes the war and immigration and the courts.
Sen. Frist's break with Bush on stem cells and Dobson's critique of Frist is the sign of things to come. A successful veto by president Bush against bi-partisan stem-cell bills in Congress will guarentee huge Democratic victories in 06, but the repricussions will extend.
Issues such as the war and stem cells will drive moderate Republicans to push for Guliani or McCain in early primaries and put up a fight in other primary states.
The result: Religious conservatives will balk at their loss of effect on the Presidential nominee... and pressure for a third-party conservative to run for President. Due to their absolute focus on the courts, abortion, and stem-cells, Dobson and others will find a third-party candidate if they cannot get a conservative the Republican nomination. Could be Moore from AL, a dark horse conservative, Allen from VA? Not sure yet.
Also look out for a Tom Tancredo independant bid at the White House over the issue of Immigration. This bid could peal both Dems and Reps but I think more Reps than Dems.
Bush has created such a volitle nation that third-party, independant bids are only natural. Think of Perot running in '92 for fiscal reform and Wallace in '68 peeling off Dixiecrats in the South over segregation and "Law and Order" politics.
2008 is a long ways away, and the Bush veto on stem cells may not hold and take it away as an issue, but the Tancredo-Immigration idea is real for '08 and who knows what else.
I simply do not think that Americans will settle for just Democrat or Republican for President in 2008, and I think that plays well for the Democratic candidate with a Republican president out-going.