Obama is the quite conceivably the worst president in US history, and anyone that honestly thinks that a Democrat running on his record can win office either has rocks in their head, or it's time for another revolution. I'm going to bet the former rather than the latter.
“Somebody” may have said Reagan couldn’t win, but in 1980 it had only been 4 years since two consecutive Republican POTUS terms.
Nixon won 60% of the vote in 1972. And Ford, a very weak candidate with the Nixon “baggage” only lost to Carter by 3 percentage points.
America was a very different demographic then.