The country is just too bitterly divided along social lines for economic prosperity to deliver one candidate a landslide (assuming a landslide in the popular vote means at least 10% margin of victory.)
Assuming that
the US does in fact hold a nationwide presidential election in 2020,
the Democratic & Republican parties get > 90% of the votes in 2020, and
US military fatalities in new, unprovoked, foreign wars are minimal (< 3000),
I predict:
a Trump landslide with probability 20%, assuming 2% weighted growth over Trump's term
a Trump landslide with probability 70%, assuming 3% weighted growth over Trump's term
a Trump landslide with probability 95%, assuming 4% weighted growth over Trump's term
using your definition of landslide, and defining "weighted growth" as annualized growth in quarterly, inflation-adjusted, disposable, personal income per capita, with recent growth weighted more heavily with a discount factor λ of 0.9. (See Hibbs for more details.) This is a clear prediction.
I'm more doubtful of chatter about rising political polarization than I am about fundamentals-based models of voting, and those models highlight the economy & war as the factors that most matter. As such I reckon sufficient economic prosperity could in fact produce a landslide for Trump (and virtually any incumbent, really).
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