Donald Trump did things no presidential candidate has ever done before, such as publicly mocking a reporter’s disability. Photo: Screenshot via CBS

In 2016, a presidential candidate who broke just about every rule about who is qualified to run for president and how a successful campaign should be run improbably won the GOP nomination, and then the presidency. More than two years after the fact, it’s still hard to understand how it all happened.

And now, as Democrats look for a challenger to Donald Trump’s reelection in 2020, an enormous field of potential candidates is forming — one that could overwhelm a nominating process designed to choose among relatively few rivals and produce a contested convention whose prize is fought over by a divided party. I can’t imagine that the two phenomena are not closely related.

It’s true that Trump blew up an awful lot of conventional wisdom. He’s the fifth president to have never won a previous elected office. But three of the others (Zachary Taylor, Ulysses Grant, and Dwight Eisenhower) were military heroes, and Herbert Hoover was a universally renowned humanitarian as the organizer of food aid to Europe during and after World War I, and then a two-term cabinet member and favorite of party insiders. Trump’s background, featuring multiple business failures and broken marriages and admitted serial adultery was unusual, too. And the way Trump campaigned was even more unprecedented, featuring nasty personal attacks on members of his own party (beginning with his mockery of the war service of his party’s most notable military hero, John McCain) and his frequent profane and belligerent utterances, alongside lies too frequent to count. And Trump also defied the ideological orthodoxies of his very ideological Republican Party by opposing the Iraq War and free trade. Yet he won.

The 45th president’s success was all the more shocking because he achieved it at a time when political scientists, practitioners, and pundits were in unusual agreement about the formula for success in a presidential nominating contest. Encapsulated by a much-quoted 2008 book, The Party Decides, the CW made endorsements from party insiders and elected officials the sine qua non of a winning presidential campaign — all the qualities that Trump lacked and that one particular rival he trounced, Jeb Bush, had in surplus. He went on to overcome all the conventional advantages — in money, political experience, hotshot advisors and elite approbation — that Hillary Clinton had over him in the general election as well.

And so there’s an inchoate sense that Trump broke the mold so thoroughly that anybody can run a viable race for president, perhaps successfully. That’s how you get multiple billionaires with no record of public service (e.g., Tom Steyer, Howard Schultz, and Mark Cuban) seriously considering candidacies; seven sitting Members of the U.S. House, which hasn’t produced a president since 1880, exploring presidential runs; mayors from municipalities as small as South Bend, Indiana (Pete Buttigieg) getting encouragement to run; septuagenarians galore (Bernie Sanders, Joe Biden, John Kerry) looking for a fountain of youth; and politicians best known for respectable losses in statewide races (Beto O’Rourke and possibly Stacey Abrams and Andrew Gillum) making 2020 lists as well.

No, all these people won’t run, but few if any authoritative voices are telling them it’s a waste of time. One rich celebrity who did take himself out of the running, actor Dwayne “The Rock” Johnson, summed it up well:

“I think in a lot of people’s minds, what Trump has proved is that anybody can run for president,” Johnson says. “And in a lot of people’s minds, what he’s also proved is that not everybody should run for president.

That second part needs to be heard a bit more often. For one thing, Trump in 2016 had an asset that few potential candidates (even The Rock) possess, which is decades of heavy national publicity as a popular entertainment figure and as a very public businessman. He also had the corner on an high-value ideological position that virtually none of his intra-party rivals shared in his virulent opposition to comprehensive immigration reform, amplified by his dangerously blunt appeals to white Christian nationalist sentiments. It is unclear there is a “lane” in the 2020 Democratic presidential landscape that is equally open and undervalued by other pols.

And let’s face it: Trump got lucky. The 16 candidates he initially faced in the GOP contest gave him an excellent opportunity to remain viable as his support slowly grew. Had either Marco Rubio or Ted Cruz gotten a one-on-one shot at Trump a bit earlier in the contest, the mogul would have probably lost. As for the general election, no matter of Russian interference or Clinton email obsession would have gotten Trump into the White House if Hillary Clinton’s campaign had invested appropriately in Michigan, Pennsylvania, and Wisconsin.

Yes, the conventional wisdom so neatly and confidently presented in The Party Decides has been shredded. More likely, though, Trump ‘16 was the exception that proves rules do exist, and a new, if modified, conventional wisdom that does make sense will emerge.

But politicians have always been willing to gamble on luck, and the phenomenon of a huge field of gamblers paradoxically makes the odds of something strange happening that much stronger. Democrats who don’t want to roll the dice in 2020 might want to consider ways to winnow their field before voters vote and we find out that there are not “three tickets out of Iowa,” as legend has it, but maybe ten. Thanks to the strange man in the Oval Office, a broad array of Americans are seeing the next president of the United States in the bathroom mirror each morning. Maybe all of them would represent an improvement over the incumbent, but it could be perilous to give them all a clean shot at the job.