Over the last couple of weeks, as the once-unwieldy Democratic presidential field whittled itself down to a duel, Bernie Sanders’ detractors have begun to insinuate that the senator from Vermont is the liberal mirror image of Donald Trump.

“If you think the last four years has been chaotic, divisive, toxic, exhausting,” then-candidate Pete Buttigieg warned in his valedictory appearance on the Democratic debate stage in South Carolina, “imagine spending the better part of 2020 with Bernie Sanders vs. Donald Trump.”

Surrogates for Vice President Joe Biden quickly doubled down on that theme, suggesting that Sanders’ progressive policy views camouflaged a narcissistic candidate nearly as rigid, arrogant and dismissive of women as the Republican president he loves to vilify.

This is unfair. It’s true that Sander’s angriest, most disaffected disciples bear a startling resemblance to Trump’s perfervid base. But to equate Sanders’ pedantic populism with Trump’s myriad pathologies — his nonstop mendacity, his casual cruelty, his delusional exaggeration of his own capacities — is to ignore the differences between a cold and a cancer.

I’ve never voted for Sanders. But I’ve never believed he posed a mortal threat to the republic.

His bombast can be annoying, even in small doses. But Trump’s deficits are genuinely terrifying, especially when a crisis highlights their severity.

And while congressional and judicial oversight would almost certainly constrain Sanders’ conduct as president, it’s unclear that either can withstand Trump’s relentless challenges to constitutional order.

After Biden’s triumph on Super Tuesday II, it’s unlikely that I and other Michigan voters will be forced to choose between Trump and Sanders. Although he has yet to be mathematically eliminated, Sanders’ disappointing performance in Michigan all but dashes his hopes to capture the Democratic nomination.

But Sanders still has an opportunity to prove that I and others were right when we rejected those facile comparisons between him and Trump.

If Sanders believes what he has consistently argued — that Trump’s tenure has been an American tragedy, and that his re-election would extinguish reproductive freedom and civil liberties while crippling efforts to expand health care, reduce economic inequality and slow the pace of climate change, his obligation to suspend his campaign is clear.

And he needs to take that decisive step in a matter of days, not weeks, joining the rest of Biden’s erstwhile rivals in a united Democratic campaign to reclaim the White House.

Every day Joe Biden spends parrying Sanders’ increasingly desperate attacks on Biden’s 44-year voting record is a day squandered in the campaign to hold Trump accountable for his administration’s ongoing incompetence. Every news cycle consumed by arguments over “Medicare for All” is a news cycle in which Trump’s evisceration of the nation’s public health infrastructure goes unchallenged.

The need for Democrats to sublimate their intramural rivalries and suspend pointless ideological tests in the face of that challenge is urgent.

But surely Sanders has the reason and character to make a proper choice — one that recognizes how dramatically the political landscape has changed with his defeats in Michigan, Mississippi and Missouri, and how much his country’s dire circumstances have eclipsed his own.

With a single, realistic act, he can debunk the cynics’ blithe assertion that all populists are alike. By ending his campaign now, he can show the world that the divisive poison threatening the United States has been contained to one party — and that he and his Democratic allies mean to arrest its spread.

Brian Dickerson is the editorial page editor of the Detroit Free Press. Contact him at bdickerson@freepress.com.