A warning to progressives: How bad can it get?

Very, Bad, Indeed.
I have read numerous diaries, from numerous well known progressive  commentators, such as Cenk Uygyar, who posts here frequently, blasting Obama for any number of things, like "selling out his followers,""not fighting for health care reform,""not supporting Gay Rights by not fighting against DADT,""not fighting for global warming legislation," and on and on.
It is one of the great issues of DailyKos about the spectrum of Obama bashing / categorical support should take place. Should we support his mild liberalism? Or just throw him under the bus, "the way we have been thrown under the bus," etc. etc. Personally, I believe that things can get bad in the USA, very bad, inconceivably bad, and before we start bashing, we should think twice with a long-term perspective on our situation.
I will turn to history and a book I have recently read, "The Nightmare Years," by William Shirer, and the Spanish Civil War, to clarify the issue.