Donald Trump is the most unpopular candidate in the history of modern polling, with about 60 percent of voters rating him unfavorably, putting him roughly 23 points under water. (Hillary Clinton, currently being battered by yet another round of potentially damaging email revelations, is only a pinch less unpopular.)

In fact, Trump has turned out to be such a surprisingly weak candidate, it seems possible or even plausible that Bernie Sanders, had he won the Democratic nomination, might at this very minute be mentally measuring the drapes for the Oval Office — if Sanders cared about such things. After all, as Sanderistas liked to point out during the primary, Bernie consistently beat Trump in hypothetical matchups by wider margins than Clinton.

So in the parallel world where Sanders beat Clinton and Trump still won the GOP nomination, would Bernie be crushing Trump? If the presidential race were a likability contest, almost certainly. But if it were just a geniality pageant, Sanders would probably have won the Democratic nomination.

Let's imagine a Trump-Sanders general election. It would be fascinating for many reasons, but let's start with political parties, because Sanders isn't technically a Democrat and Trump is barely a Republican. Based on the polling and exit polls from the primaries, it's pretty safe to say that Sanders would have the millennial vote sewn up, and white liberals, too. Sanders is a senator, a former congressman, and a one-time mayor, but he is clearly more of an outsider than Clinton — and, because he isn't a millionaire, he's also in many ways more of an outsider than Trump. He would be a change agent — remember the political revolution? — who's also embraced by a popular sitting president.

On the other hand, it's hard to see Sanders winning much Republican support, even among Republicans disgusted by Trump. This might have helped Libertarian Gary Johnson — in the parallel world, he doesn't have Aleppo moments and runs a solid campaign — but it's hard to see Green Party nominee Jill Stein getting even her current 2-3 percent. Most Republicans would probably have stuck with Trump, as they are now, and most Democrats would likely have felt the Bern, enthusiastically or not. It would have been an embarrassment of riches for independents.

Policy-wise, Trump and Sanders actually have more in common than Trump and Clinton — both are notable trade skeptics, for example, and each is comparatively wary of involving the U.S. in foreign adventures. But Trump is what you might call an opportunistic populist — he seems willing to tailor his policies to the mood of his electorate — while Sanders is more of an ideological populist, driven by ideas more than political calculations, at a time when some of his big ideas struck a chord. Sanders, a self-identified European-style democratic socialist, is to the left of most Americans. Trump is a mixed bag.

Trump has been relatively consistent on building a Mexico border wall and keeping out Muslims, but would he have shaped his other views to contrast more with Sanders and appeal more to the political center-right? Maybe. Clinton, though her policies tend to be significantly further to the left than Bill Clinton's in 1992, takes up such a big swath of the pragmatic center temperamentally, there isn't much room left. Facing Sanders, it is easier to imagine Trump actually following through with his often-promised, only briefly attempted pivot. That point in September, before the first debate, is the only time in the general election he came close to passing Clinton in the polls.

It's hard to see Sanders — who "honeymooned" in Soviet Russia — exploiting Trump's coziness with Vladimir Putin like Clinton has, especially given his own sympathies for Cuba's Fidel Castro and Nicaragua's Daniel Ortega. But Sanders would likely have done about as well as Clinton among Latinos, crushed Trump among African-Americans (though perhaps not as definitively as Clinton will), and done better than Clinton among the white working-class voters who make up the bulk of Trump's support. Sanders would have robbed Trump of a good share of the anti-Clinton vote while also, presumably, getting the lion's share of the anti-Trump vote.

But — and here's where things get tricky — it's not clear the anti-Trump vote would have been as big as it is today. Remember, Donald Trump is a natural performer. He can be affable and entertaining on camera and on stage. Most of his problems since the Republican National Convention have been of his own making, often with a big assist from Clinton, who has shown a remarkable ability to get under Trump's skin.

Would Sanders' Democratic convention have given the stage to Khizr and Ghazala Khan, sparking Trump's first general-election crack-up? Maybe the Access Hollywood tape would have emerged, but if Clinton hadn't baited Trump into picking a fight with former Miss Universe Alicia Machado beforehand, would Trump have been able to survive an 11-year-old video relatively unscathed? Would Sanders have beaten Trump in all three debates? I don't find it plausible that the Clinton campaign arranged for 12 women (and counting) to come forward with stories of Trump's groping and assault over decades, but Hillary clearly helped guide Trump's foot into his mouth. That doesn't seem like Sanders' modus operandi.

That's the downside of having "likable" be your brand. If this had been a positive, issues-oriented campaign, like Sanders pledged to run, we might not have learned so often or clearly how temperamentally unfit Trump is when faced with the slightest adversity or challenge to his authority. For all the grousing about how ugly a campaign this has been — and it hasn't been pretty — goading Trump into showing his thin skin was a real service to the republic.

At the same time, we never got to see how Sanders would have reacted to the opposition-research trove Trump would have dumped on him. Trump has a bully's instinct for belittling and humiliating people he thinks are weak. Amazingly, he hasn't been able to rattle Hillary. Is Sanders as unflappable? We don't really know.

And of course, "we don't really know" is the only true answer we'll get to the question in this headline. Sanders could have relegated Trump to the dustbin of historically humiliating losses, or Trump could have ground Bernie into so much Vermont dust. In a not insignificant way, Sanders got the best of all worlds: He's still the nice guy, he's world famous, and in that parallel universe, he might even be president. In this world, being a U.S. senator in a safe seat is a pretty sweet gig.