On page 71 of “How Democracies Die”, Levitsky and Ziblatt write that the 2016 election “was essentially a toss-up [because of] partisan polarization…the uneven state of the economy and President Obama’s middling approval ratings.” 

It was not a toss-up. At all times Clinton was highly likely to win a national victory. But that mattered not at all. At all times Trump was likely to win an electoral college victory, because he had the freedom, as a wild card candidate, to craft a message exclusively designed for the swing states.

Also, Obama had good approval ratings.