Republican nominee Donald Trump with campaign chairman Paul Manafort in Cleveland in July 2016. Rick Wilking/Reuters) (Rick Wilking/Reuters)
Opinion writer

The assumption of both parties, the mainstream media and activists on both the right and the left has been that President Trump would run for reelection and very likely win his party’s nomination.

However, if we collectively think Trump is in as much trouble as court filings from both the special counsel and the U.S. attorney’s office for the Southern District of New York suggest, it is not unreasonable to consider that he might resign or not run for reelection. Likewise, he might insist he’ll be vindicated and run, but lose the nomination (which has never happened, though Lyndon B. Johnson dropped out in 1968) when the GOP sees his polling numbers tank and realizes the depth and breadth of his legal problems.

What would the GOP 2020 presidential primary look like without Trump? Chaotic, for one thing. There could well be a flock of candidates, falling into one of five categories.

Vice President Pence is his own category. A stiff, nearly robotic figure who has tied himself to Trump with nauseating sycophancy would certainly not be the favorite. Proximity to Trump, if things are so bad he isn’t running in 2020, would be political death. (Specific questions about what Pence knew and when he knew it could also hobble him.)

The second category are those loyal Trumpists who would be Trump — but without the lawsuits, prosecutors, conflicts of interest and thick-headedness. In this category, you’d put the comically ambitious Sen. Tom Cotton (R-Ark.) and a flock of Freedom Caucus members, as well as those Trump supported for office (e.g., Georgia Gov.-elect Brian Kemp). They would have the task of staying loyal to Trump to inherit his base and distancing themselves so as not to be tainted by him. Good luck. If Trump goes down, those who enabled and echoed him uncritically, in all likelihood, won’t be viable candidates.

The next category are those Republicans who backed Trump’s policies, but put a modicum of distance between themselves and Trump — and did so without incurring the president’s wrath after the 2016 election. Sens. Ted Cruz (Tex.), Rob Portman (Ohio), Tim Scott (S.C.), Ben Sasse (Neb.), along with a whole bunch of other conservative senators or governors would fall into this category. They would test the proposition of whether the pre-Trump agenda of supply-side tax cuts, hostility toward government and cultural issues — including staunch opposition to comprehensive immigration reform — would fly. (They’d have to figure out how one can be skeptical of government and wear the moniker of conservative while racking up tens of billions in debt.)

Then there are the dissidents who actively criticized Trump, but didn’t have much problem with his actual agenda. Republican Sens. Bob Corker (Tenn.), Jeff Flake (Ariz.) and, to an extent, Mike Lee (Utah) let it be known that they thought Trump unfit for office and found his nativism and fondness for dictators dangerous. However, they were generally pleased with judges, tax cuts, deregulation and efforts to repeal Obamacare.

Finally, those who see that the problems of the GOP and its agenda go well beyond Trump might choose to run on their formula for reformation. In this category are successful governors (Ohio’s John Kasich, Maryland’s Larry Hogan and Massachusetts’s Charlie Baker). They stress bipartisanship, a governmental role in health care and combating climate change and fiscal responsibility. Kasich (or others) might bail out of the party altogether and start a new movement or party.

In sum, this hypothetical presidential primary there could well be a battle among those who think Trump was betrayed, those who think Trump is an isolated blip in the history of the country and party and, finally, those who think the GOP needs a makeover to be attractive for a 21st-century electorate. Then again, this robust debate might be deferred until 2024 if, in the face of common sense and simple decency, Republicans sign onto four more years of Trump and his circus.

Read more:

Greg Sargent: As Trump slides in a new poll, reality begins piercing the bubble

Marc A. Thiessen: What Trump needs to do to avoid being a one-term president

The Post’s View: Russia’s support for Trump’s election is no longer disputable

Ann Telnaes: Trump is feeling squeezed