Don't want to keep repeating what I have already said in this thread. There is a reason why Obama was elected right after the mess that Bush junior created and why he won against Romney (even though someone else was throwing up random numbers at me)
There are multiple reasons, actually. The biggest one in my eyes was this one, though:
While his actual work as president is certainly more debateble and controversial, there is no doubt that Barack Obama was extremely good at campaigning. He had the necessary charisma, likeability, story and especially the rhetoric ability (speeches with substance, but not overcomplicated) to mobilise masses (especially the minorities) to follow and vote for him.
IMO this race was not so much won by Trump, but lost by Clinton. For that I only need to look at one statisitc, which is total votes in favour of the candidates.
Donald Trump will be walking into the oval office while having less total votes in his favour than McClane 2008 and Romney 2012.
The divide of the democratic party and votership and the poor way Clinton came across for many people (cold, calculating, untrustworthy) lead to many people either voting for a third party candidate or not turning up altogether. This loss of votes turned out to be critical for her.
Put Obama in Clinton´s place and the vote ends in a landslide in the other direction.