The Dems stood for nothing in the last election other than "I oppose anything Bush favors." Not a way to win an election. You need to stand for something. There is nothing wrong with ripping Bush, as long as you propose a solution. They didn't do that. They just said, "I have a plan." That is fine, but they did not expand on that plan other than to say, "I was in Vietnam."
On your other point: there is no question that the Reps and Dems will attack anyone who is moderate. I heard this during the last election, and they will increase those attacks as they start to lose control. I can speak on the PA state level of the Libertarian Party, and they understand the concept of providing solutions. They know that attacks with no solutions spells failure. There is emphasis on informing voters of the benefits of electing Libertarians and what they can provide to the constituents.