Some Rep voters will stay home, sure, but they will more then be made up for by the Independents who are strongly for JM and even Democrats who will vote for him in greater numbers then they have ever voted for a Republican.
It is you who fail to grasp the damage the Democrat party has done/is doing itself. You, like many think they can wave a magic wand and make all that has happened in the past year simply go away. You also have the idea, a very human failing, that because YOU feel a certain way certainly most if not all will feel the same way. It's the wrong idea and you will find this out.
In the end I foresee at least half the Republicans who so stridently claim they will stay home rather then vote for McCain will return to the fold when the prospect of uber liberal WH becomes real.
1. McCain will choose a woman or a black as his running mate.
2. If Obama gets the nod, he will have a woman as his VP.
3. If Clinton gets the nod, she will have a black as her VP.
4. McCain will win the general decisively.
5. McCain will either pass away or step down before the end of his 1st term and his VP will become the first woman and/or black President.
6. Dems will hold the House, but the Senate is a big question mark.
7. Two Supreme Court Justices will step down within a year of McCain taking office. A third will pass away/quit before the end of his first term.