When the 2016 election rolled round, a surprising result emerged. According to the model, Donald Trump should have received 54.1 percent of the vote; in actuality he received 48.8 percent. I'm quite confident that the gap was a function of the generally unfavorable rankings on Mr. Trump's personal qualities. In other words, a more "normal" Republican would likely have won the popular vote by a substantial margin (instead of losing it by three million votes).
A good part of Mr. Trump's edge in 2016 was the incumbency factor — after eight years of a Democratic president, voters would ordinarily have wanted a Republican. (Since 1952, only one man has become president following eight years of a president of the same party.) In 2020, incumbency will be a tailwind for Mr. Trump as the vast majority of presidents are chosen for a second term.
In its present state, the economy will also be helpful to the president. All told, Mr. Trump's vote share would ordinarily be as high as 56.1 percent. But that's before factoring in his personality. As recent polls show, if the election were today, he would lose to most of the Democratic hopefuls by a substantial margin;
in the case of Joe Biden, by nearly eight percentage points.