One critical, mostly overlooked fact of this election is the appointment of new Supreme Court justices. Currently the court is fairly balanced, but 'right' leaning due to the Bush appointments. Currently Ruth Vader Ginsberg, David Souter and Antonin Kennedy are the most liberal justices. Unfortunately, they are also the most likely to retire in the next 4 years.
Regardless of your political affiliation, it is in America's best interest to have a balanced court. A balance between liberal & conservative justices will encourage rigorous discussions of the matter before the court, and helps to ensure the interpretations of our constitution, and precedents that follow are more likely to protect constitutional rights.
If Senator McCain is elected he will upset this delicate balance by appointing justices that have a conservative background ( AKA GOP leaning).
This would be a tragedy for America. A conservative Judiciary would likely further the attacks on our civil liberties, and accelerate this countries move to the extreme right.
I do not profess to be educated in legal matters, especially when it comes to the highest court in the land.
However I do l know this, whoever wins this election will determine the legal landscape of America for the next 3 decades.