Irrefutable Point IV: Trump's Enormous Incumbent Vote Gain
In 1888, Grover Cleveland, the first Democrat to occupy the White House since the Civil War ended, gained 620,000 net new votes over his winning popular vote total from 1884. Running against Benjamin Harrison, he managed to lose his home state of New York, and though he won the popular vote, was edged out in the Electoral College.
The Empire State revolting against the incumbent gave Cleveland the unique distinction of being the last incumbent to gain votes from his previous election and lose his campaign for reelection. By 1888, the growth of the Republic had slowed, with most of the union having formed by that time. Popular vote totals were steadier and more predictable, with only tiny territories yet to be added as states.
It makes perfect sense that gaining votes in a reelection campaign would doom any challenger’s campaign, especially if “stability voters” are pleased with the incumbent’s performance and break away from normal party lines, setting the challenger’s party back from its normal base starting point.