DDM, did you read the recent LA Times article on Trump winning? It touches back on that and shows the current numbers and how Trump can win (he's currently ahead) in 2020, but also how it can potentially go South for him rather quickly in 2020. Link
"Trump’s apparent margin of victory can be strengthened by a few more really good quarters of economic growth. Specifically, for any calendar quarter in which economic growth exceeds the long-term average of 3.2%, the incumbent picks up an additional four-fifths of a point in the popular vote. So far, Trump has enjoyed three such “good news” quarters. They have added almost 2.4 points to his predicted vote share. Fair predicts those good quarters all but assure a Trump victory in 2020.
But Trump does have something to worry about. Economic forecasters are nearly unanimous in predicting an economic slowdown as the effects of the Trump tax cuts and Fed interest rate cuts dissipate. Many economists are predicting a recession in 2020. The trade wars that Trump has initiated may also spark unwelcome price hikes. If economic growth turns negative and inflation rises, Trump’s predicted margin of victory shrinks quickly. -snip
He also has the home court advantage so-to-speak in that more presidents have done two terms than been the 'one term losers'. So if he somehow manages to still lose even if the economy is solid in 2020, that'll be something telling.