The worst case for the republicans is Trump continues to falter, and a party split arises like 1912. Half the base wanting to ditch Trump , and half fiercely loyal to him. The split plays out among prominent politicians too. Paul Ryan is gone by this point, having been taken out by right wing freedom Caucus after losing badly in 2018.
So here is the scenario.
Cruz declares his candidacy somehwere in 2019 after GOP loses both houses in 2018. Trump approval is at 25%, but still 50-60% among Republicans. Soon thereafter John Kasich announces a campaign too.
Trump decides the Republican nomination is unnecessary for a sitting President and declares he is going it alone, meaning the Republicans will be running a candidate against Trump. Cruz wins easily over Kasich and others.
Trump get on the ballot himself in all 50 states on various ballot lines, most commonly as National Republican, or independent in States where that is beneficial to ballot access laws.
Bernie Sanders wins the Democratic primary easily after winning Iowa caucuses, Nevada caucuses, and New Hampshire by double-digits. He loses SC primary to Booker by less than 5 points, seen as a good result, and is coronated on Super Tuesday.
Senator Sanders - Democratic Party 53%, 466 ev
Preisdent Trump - National Republican 27%, 35 ev
Senator Cruz - Republican Party 18%, 37 ev
Other 2%
