The lesson was clearly that Americans like to complain about "divisive politics", but when push comes to shove are not at all averse to re-electing precisely the mix of political divisions that keep the federal government from doing anything. Anyone who claims that the election proves any other point is merely engaging in wishful thinking.
This election should remind us all of one of the peculiar aspects of the American character: how to pretend to want one thing while really wanting another. We want Congress thrown out because they're crooks -- EXCEPT for "our guy". We want government spending to stop -- EXCEPT for "our program". We want government to force conservation -- EXCEPT we want "our car" and "our lifestyle" left untouched.