I am sure I created a similar thread some time back, but here it goes:
2008: Rudy Guliani/Fred Thompson(R) V. Hillary Clinton/Bill Richardson(D)
2012: Rudy Guliani/Fred Thompson(R) V. Barak Obama/Jim Webb(D)
2016: Barak Obama/Jim Webb(D) V. Tim Palewnty/Mike Pence(R)
2020: Tim Palewnty/Mike Pence(R) V. Antonio Villaraigosa/Rahm Emanuel(D)
Interesting.
I think it'll be
2008: Romney/Bush V. Hillary/ Richardson
2012: Romney/Bush V. Obama/Webb
2016: Bush/Pence V. Webb/Ritter
2020: Webb/Ritter V. Pence/Pawlenty
You're scenario has the country swinging way right with Giuliani for the GOP and then later Obama for the Dems. I have the country staying the course with a conservative GOP ticket and later a win by two major centrist Democrats.