I think another one of the main points here is "better the enemy you know than the one you don't". If both candidates are considered bad, people will probably think, "well, we already survived one term of (insert incumbent here), so we should be able to survive another".
Sure she wasn't an incumbent technically, but by de-facto, we saw last year how that logic turned out for Hillary.
Not really. Obama's charisma and popularity was not transferable. There were many who HATED Clinton and voted against her in the primaries 8 years prior before having Obama beg these same people to vote for the same scandal-laden, boring, old white lady from 2008. The people inclined to vote for the Democrat just stayed home. Obama at his worst approval ratings would have still beaten Trump.
