The thing the Republicrats fear the most is any third party. The one party system works to well for the filthy rich and powerful.
People cower and are so afraid of voting third party it is ridiculus. If Nader started showing 7% to 10% in the polls you can be sure Kerry would do a Gary Hart pronto and some one much further to the left would replace him.
Most of the other Nations in the world have more parties than two and work through coalition governments with proportional representation. Most other Nations also saw what a mistake the war in Iraq was going to be.