Anger is almost always the changer now. That's just how polarization, negative ads, media blitzes make things turn out.
2000: Anger at Clinton for "muh Lewinksy" (if that weren't so, Gore would've actually used him and curbstomped Bush)
2004: Anger at terrorists and conspiracy theorists who think civil liberties undermine beating terrorists (hence why Kerry, an actual 'Nam veteran, lost)
2008: Anger at Bush and recession (hence Obama getting pretty far on just comparing McCain to Bush)
2012: Anger at recession and people that escaped it. (hence the 47% remark sinking Romney)
2016: Anger at recovery not being perfect (hence a bunch of people believing one catchy slogan instead someone objectively better qualified)
Makes plenty of sense then that 2020 should be defined by anger.
But anger at what in 2020? Anger at a bad economy? Anger at an immoral president? Anger at massive corruption? Depending on what it is, that changes the election significantly.