An old union song from the 1931 coal-field wars in Harlan County, Kentucky, has been rattling around my brain.

Written by Florence Reece and later popularized by Pete Seeger, it repeatedly asks the question: “Which side are you on, boys? Which side are you on?”

But what makes the song particularly apt for this spirit-numbing presidential election is this lyric: “They say in Harlan County/There are no neutrals there.”

Up until now, Libertarian Gary Johnson was neutral ground. The affable former two-term GOP governor of New Mexico, famed for his permissive attitude toward marijuana, represented a safe haven for Republicans who couldn’t vote for the bilious billionaire who has taken over their party.

Competent and capable?

On Thursday morning, The Detroit News endorsed Johnson, the first non-Republican presidential candidate the newspaper has backed in its 143-year history. In an editorial that included the subhead, “Fit for the presidency,” the News declared, “This is an endorsement of conscience, reflecting our confidence that Johnson would be a competent and capable president and an honorable one.”

[Letting Gary Johnson Debate Is Simply Too Risky]

A few hours before the newspapers began rolling off the presses, Johnson appeared on a special edition of MSNBC’s “Hardball” from the campus of the University of New Hampshire. At the beginning of the program, Johnson apologized again for not recognizing, in an earlier TV interview, the name of the Syrian city synonymous with suffering. “I blew this Aleppo question, OK,” he said. “I want to take full responsibility for that.”

But then setting up the most painful non-Trump moment in the 2016 campaign since Marco Rubio kept repeating his debate talking points, host Chris Matthews innocently asked Johnson which living foreign leader he admired.

There were dozens of acceptable answers even for a dovish libertarian. Angela Merkel could be praised for preserving the euro and welcoming Syrian immigrants. Johnson could have gushed over Aung San Suu Kyi’s fight for human rights in Myanmar. A kind word might have been said about Francois Hollande’s refusal to buckle in the face of horrifying terrorist attacks. Or Johnson could have simply noted that he had been impressed at the way that Justin Trudeau has inspired the young.

Instead, for 50 seconds — which seemed more like 50 days on live TV — Johnson offered a dramatic rendition of a blank slate. Johnson couldn’t come up with a single name other than the late Israeli leader Shimon Peres, whose obituary was in the headlines. Finally, the Libertarian nominee said wanly, “I guess I’m having an Aleppo moment.”

At that moment, Johnson’s candidacy went from plausible protest vote to comic punchline. This was a mental short circuit so severe that it’s impossible to laugh off or tweet away with campaign lines like, “Detroit News endorses Johnson. Who’s endorsed Trump? Hmm … brain freeze.”

Voting for Johnson at this point seems about as sensible an option as writing in “Puff the Magic Dragon.”

Voting for Johnson at this point seems about as sensible an option as writing in “Puff the Magic Dragon.” The only other non-Trump option for principled conservatives is squandering a protest vote on behalf of the quixotic and nearly invisible candidacy of former covert CIA agent Evan McMullin.

Desperately seeking alternatives…

It is an indication of the desperation that many feel about this election that the Chicago Tribune endorsed Johnson on Friday morning without ever mentioning Aleppo or “brain freeze.” Instead, the Tribune hailed Johnson and his running mate, former Massachusetts Republican Gov. Bill Weld, as “agile, practical and … experienced at managing governments.”

Sorry, but after watching that Johnson interview with Chris Matthews, it seems a stretch to call him “agile.” The unavoidable truth is that the idea of Gary Johnson remains far more appealing that the reality.

This is — sadly enough for the nation — the most unequivocal “Which side are you on, boys?” election since the Civil War.

Monday night’s debate should have erased the last naive illusions that Donald Trump is anything other than an unhinged buffoon whose ignorance is only exceeded by his arrogance.

[Donald Trump and the Second Battle of the Sexes]

It all comes down to the patriotic question: Do we, as a nation, want to entrust the nuclear codes in a hair-trigger world to a man who obviously doesn’t care about anything beyond his Titanic ego — a man who refuses to listen or learn, even when the presidency itself is on the line?

Yes, there are Republicans who sincerely respond to all criticism of Trump with the four desperate words: “But the Supreme Court …”

The problem with that argument is Trump’s character or the lack thereof. It is baffling why anyone — even the craven Ted Cruz — would believe a list of would-be Supreme Court nominees provided by a man who has reneged on every business deal in his life. Is anyone still clinging to the ludicrous fantasy that once he hits the Oval Office, Trump’s word would suddenly become his bond?

Hillary Clinton, for all her flaws and ethical lapses, is the only 2016 candidate offering that rare commodity called sanity. Conservatives will not like most aspects of her presidency — and even left-wing Bernie Sanders’ acolytes are apt to be disappointed.

That’s what happens in a democracy when your side loses to a rational opponent. You regroup and fight again in two and then four years. But Trump represents what happens in a democracy when the voters go amok. The damage from a Trump presidency would take decades to repair — if such a national fever dream could ever be erased.

So which side are you on, boys and girls? Which side are you on?

Roll Call columnist Walter Shapiro is a veteran of Politics Daily, USA Today, Time, Newsweek and the Washington Post. His book on his con-man great-uncle was just published: “Hustling Hitler: The Jewish Vaudevillian Who Fooled the Fuhrer.” Follow him on Twitter @MrWalterShapiro.