Voting third party in this presidential election isn’t merely impractical.

It’s unprincipled.

With the two most-ever disliked major-party nominees on the ballot this year, many American voters are desperately seeking alternatives, including fictional characters and dead gorillas. Young voters in particular have been shunning the two main options, with some recent polls showing that a quarter to a third plan to vote for either Libertarian Party candidate Gary Johnson or Green Party nominee Jill Stein.

The loudest arguments against casting a ballot for these third-party options rely on their unviability. These are admonitions against enabling a spoiler and effectively electing the greater of two perceived evils (usually meaning Donald Trump).

“If you vote for a third-party candidate who’s got no chance to win, that’s a vote for Trump,” President Obama cautioned this week.

Listen to a full audio recording of The Washington Post’s editorial board meeting with 2016 Libertarian presidential ticket, Gary Johnson and Bill Weld. (Mahnaz Rezaie/The Washington Post)

Sen. Bernie Sanders (I-Vt.) has repeatedly made similar remarks, urging against a “protest vote” because Americans must remember that “either Clinton or Trump will become president.”

The implication is that if Johnson or Stein had a chance of winning, voting for them would be justifiable. Righteous, even!

But these third-party options are bad candidates not simply because of their impracticality, or their underdog status, or their lack of exposure, or some nonsense about a rigged political system.

Johnson and Stein are, on their own merits, terrible, unserious choices. They are unfit for office.

This was especially evident Wednesday. Johnson had whined about being denied a place on the presidential debate stage. So MSNBC gave him a giant prime-time platform from which to make his case.

It didn’t go well.

“Who’s your favorite foreign leader?” MSNBC’s Chris Matthews asked.

Green Party presidential candidate Jill Stein stopped by The Washington Post on Aug. 25, taking reader questions from Facebook explain her efforts to build out the Green Party on the local level, her presidential bid and clearing up her position on the usage of vaccines (Adriana Usero/The Washington Post)

“Who’s my favorite?” Johnson responded, with a blank stare.

“Anywhere in the continents,” Matthews said. “Any country. Name one foreign leader that you respect and look up to. Anybody.”

Johnson could not name a single foreign leader worthy of respect. He rambled about a former president of Mexico — which shares a border with the state Johnson previously helmed as governor — but then could not recall which Mexican president he was thinking of.

Johnson chalked up the whole incident to another “Aleppo moment,” referring to an earlier time when he embarrassed himself by not recognizing the name of a besieged Syrian city. His immediate, self-deprecating apology after that flub was refreshing; hey, we all have brain freezes sometimes.

Given that blunder, though, Johnson should have expected further prodding about his foreign policy knowledge in future interviews, and boned up. Instead, he apparently found it acceptable to claim another “Aleppo moment.” Note: It’s never a good sign when an entire new genre of political gaffe is named after something you did.

These are hardly the only times Johnson’s apparent disinterest in learning about the world around him have proven him unworthy of the presidency.

Questioned about apparent terrorist incidents in New York and Minnesota this month, Johnson responded, “Well, first of all, just grateful that nobody got hurt.” The attacks had collectively led to dozens of injuries, which was widely reported.

Then there was that time in June, when an aide directed Johnson to a room named for Harriet Tubman, and Johnson replied, “Who’s Harriet Tubman?”

And his bonkers comments arguing that man-made climate change is real but that there’s no point in trying to stop it because “in billions of years, the sun is going to actually grow and encompass the Earth.”

Or the time he high-fived George W. Bush about the fact that neither of them knew anything about anything. “Not one thing,” Johnson recounted proudly, when introducing his fellow anti-egghead at a rally.

Johnson’s campaign tries to spin such ignorance and anti-intellectualism as proof that he’s “a real person.” And it’s true, he is a real person — just one who happens to be unprepared for the presidency.

So what about Stein? In brief: Despite being a medical doctor who knows better, she’s pandered to anti-vaxxers; expressed strong stances on high-profile issues, such as Brexit, only to abruptly reverse herself without explanation; and (along with running mate Ajamu Baraka) trafficked in conspiracy theories, among other disqualifying behaviors.

And independent latecomer Evan McMullin? (Who?) The most memorable thing he’s done thus far in the election is to accidentally pick the wrong running mate.

These candidates have received relatively little media scrutiny, let alone attacks from competitors. This allows many Americans to think of them as the purer choices for the presidency. If all the mudslinging misses them, their feet of clay go unnoticed.

Which is precisely why they probably haven’t felt the need to do their homework. If you give them your precious vote, you haven’t done yours, either.