Remember when half of American white males over the age of 40 declared themselves for the Republican presidential nomination in 2016? There were so many candidates that they couldn't fit them all on two packed debate stages. One guy stayed in after receiving a grand total of 12 votes in the Iowa caucuses; in New Hampshire, Jim Gilmore's showing improved to 133, an unprecedented 1,000 percent increase. Reader: He didn't withdraw for another six days.

Since Donald Trump is our incumbent president, and will thus almost surely be the GOP nominee in 2020, we should be spared a repeat, and really ought to be able to give our undivided attention to the approximately 437 mostly Social Security-eligible senators, governors, congressmen, mayors, and billionaire activists looking to run on the Democratic ticket in 2020. Unfortunately, Trump will almost certainly be challenged, either in the ostensibly meaningless Republican primaries or by one or more independent right-of-center candidates.

Stephen Bannon thinks 2020 will be a proper three-way race. #NeverTrumpers are already ferreting around for someone to challenge the president for the GOP nomination. "I just finished reading a book about the French resistance. It reminds me of that. People are meeting over their garages — their ateliers — trying to figure out who's going to do it," one of them told New York recently.

Here are five people who might just fit the bill.

1. John Kasich

Background: Two-term governor of Ohio, former congressman, failed 2016 GOP presidential candidate, former talk-show host, dad-joke luminary

Chance of running: 80 percent

The outgoing governor was the last candidate to concede the Republican nomination to Trump in 2016. He ultimately refused to endorse his party's nominee. Kasich has built his reputation as a socially conservative moderate. He is one of the few GOP governors who happily embraced Barack Obama's expansion of Medicaid. His 2016 campaign focused on broad social and cultural themes like the decline of the family and the drug epidemic.

Kasich has perhaps the best chance of anyone running against Trump in official primary contests, one of which he actually managed to win in 2016. Many of his views put him at odds with the libertarian element in the GOP, but that may not matter. Still: The only candidate in American history to mount a successful primary challenge to the sitting president of his party and win election afterward is James Buchanan, who kicked Franklin Pierce to the curb just before the Civil War. A more likely outcome is that a sustained but ultimately failed primary bid from Kasich destabilizes Trump's coalition, especially in the Midwest, and throws the presidency to a Democrat. Something similar happened to Gerald Ford in 1976 and George H.W. Bush in 1992. Which might be the point. Trump should be careful here.

2. Jeff Flake

Background: Lame-duck Republican senator, moaner about government waste, guy with Dickensian surname

Chance of running: 40 percent

F.H. Bradley defined metaphysics as "the finding of bad reasons for things we believe upon instinct." Most anti-Trump Republicans in Congress have distinguished themselves over the last two years by finding lame "constitutional" or "principled" reasons for implementing the worst aspects of Trump's agenda while opposing the bits that are good — his inchoate instincts on trade and his refusal to empty cant about democracy promotion in discussions of foreign policy. Last week Flake attempted to block votes on some of Trump's judicial nominees in the hope of forcing the Senate to entertain a meaningless hand-waving piece of legislation concerning the special counsel investigation. It was self-aggrandizing and pointless and a perfect illustration of his character and priorities. Meanwhile his colleague, Sen. Tim Scott of South Carolina, drew attention to the fact that one of the nominees had a history of supporting measures designed to disenfranchise black voters, sinking Thomas Farr for good. Priorities!

Flake is leaving the Senate at the end of the year and would have absolutely nothing to lose by teaming up with a rogue billionaire or two and running either in GOP primaries or as a conservative independent. He's already mucking around in New Hampshire, though he has given mixed signals about his intentions there. If he did run, the press would drool over this hero of our time, America's last honest conservative. He probably wouldn't win any states, but, again, he wouldn't really expect to do so.

3. Ben Sasse

Background: First-term Republican senator, former consultant, university president, and alleged "historian"

Chance of running: 25 percent

Everything that can be said about Jeff Flake can also be applied to Ben Sasse. But there are two crucial differences. One is that Sasse is even more of a pompous gasbag. He is the kind of pseudo-intellectual who does his history Ph.D. on Ronald Reagan. He moans about how the youth don't try hard at lame teamwork activities like decorating campus Christmas trees. The other thing that separates him from Flake, and makes it somewhat less likely that he will run against Trump, is the fact that he is a sitting senator. The position of Republican leadership is clear: Trump is the president and the de facto head of the party. Going rogue wouldn't do Sasse any favors in the upper chamber.

4. Ted Cruz

Background: Recently re-elected senator, former Texas solicitor general, Bush administration lawyer, and debate team nerd

Chance of running: 35 percent

What is there to say about Ted Cruz? The most widely loathed Republican in the Senate made a bizarre last-ditch effort to steal the Republican nomination from Trump during the GOP convention in 2016 by insisting upon the observance of a handful of arcane procedural rules. No one cared. When Trump, who previously accused Cruz's father of having conspired to assassinate John F. Kennedy, endorsed "Lyin' Ted" for re-election to the Senate, it was probably meant as a passive-aggressive insult. Cruz clearly hates Trump, whom he will never forgive for taking away the only thing he has wanted in life since he was a teenager. Because his second term won't be up until after the 2020 election and, more important, because he is roundly despised by his colleagues anyway, Cruz would have far less to lose by challenging Trump, either in the primaries or in an outsider bid. The biggest downside to a possible Cruz run? The 0.000000000007 percent chance of a Cruz-Beto O'Rourke presidential rematch.

5. Evan McMullin

Background: Former low-level CIA operative and minor GOP House staffer, failed 2016 independent conservative candidate

Chance of running: 30 percent

I will never forget the morning that Evan McMullin's candidacy was announced in August 2016. He had fewer than a thousand followers on Twitter at the time.

Sure, his campaign is best remembered for coming in third in his home state of Utah despite having led in at least one poll and later stiffing a bunch of longtime GOP hangers-on for their useless last-minute consulting work. But what else is he going to do with his time these next two years?

Besides, McMullin has at least one other thing going for him. According to Future Wikia, a website that collates possible versions of what the world would or could be like years from now, there is a parallel universe in which McMullin is nominated by the Constitution Party in 2020. Unfortunately, in this version of reality, the sitting president is Mike Pence, not Trump, which means that even in the fake future McMullin has no chance of unseating the man he ran against in 2016 in our humble but, alas, real universe. Still, I think there's a decent chance McMullin appears on MSNBC at least once in the next two years to discuss the crack team of GOP campaign hacks, neoconservative opinion columnists, and a lone Bush-era former acting deputy assistant secretary of defense for civilian personnel policy he has assembled for his prospective White House Cabinet. Godspeed!