I think Romney, aided by a GOP Congress, probably does more long term damage to America than a second term Obama, opposed by a GOP Congress.
For a present day small example of Romney already actively working to undermine our Constitution simply read this thread; http://www.freerepublic.com/focus/f-news/2913133/posts
Then think of Richard Nixon and the EPA, GHWB and the Americans with Disabilities Act, both tools being used to destroy our country. Imagine the damage Romney can do in four years with a Congress that will be forced to rubberstamp his ObamaCare, EPA and ADA type plans.
Obama will be forced to fight that very same Congress.
Who is going to force him? He doesn't pay any attention to them now. He rewrites the law and not one person stands up to him.