Do you really believe that Congress will become powerless? Do you think Hillary or Obama will be able to get their way without 60 Senators agreeing?
I think the "Hillary must be defeated at all costs" argument has done nothing but bring us to the sad state we are in now with the Republican front runner as bad as the Democrat front runner.
I don't believe that the U.S. is so fragile that a single person like Hillary can destroy it. I don't believe she will propose any insane legislation, although she would be in favor of many things I strongly oppose, and even if she did it would have to be passed by 60 Senators, that means Republicans must also approve.
I think the chances of really damaging legislation, like amnesty, being passed would be greater with McCain as president than with Hillary as president. That makes McCain the more dangerous of the two.
Unlike you, I think the U.S. is extremely fragile. Hispanic immigration has made CA permanent Demon territory, and other once-Red states are following that path. A few more years of this reconquista and it will be all over. Very few of the other immigrants flooding the rest of the country will ever vote conservative either. The Demonrat Party is unabashedly socialist, and the Pubbies are socialism lite. I look at the primary results, where RINOs won in the most conservative states left in the country. I'm afraid it's now a myth that there are millions of silent conservatives out there waiting to rise up.