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.

More Election 2020 coverage:

Joe Biden wins Michigan Democratic presidential primary

Michigan primary 2020: Full election results

That's a bum rap. It's true that Sanders' 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 non-stop mendacity, his casual cruelty, his delusional exaggeration of his own capacities — is to ignore the differences between a cold and a cancer.

Apples and oranges

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

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, Missouri and Mississippi have all but dashed his hopes of capturing 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.

A map to the off-ramp

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.

Biden boosters were doubtless disappointed Wednesday when Sanders vowed to stay in the race at least until this Sunday's debate with Biden. He said he'll use that opportunity to press "my friend Joe Biden" on his plans to address income inequality, college affordability and other issues Sanders has put front-and-center, listing 11 questions he'll ask the Democratic front-runner in their first one-on-one encounter.

That might sound confrontational, but it's also a clever and generous way to let Biden know what he needs to do to smooth the way for Sanders' graceful exit. Like a student who's been told exactly what will be on the final exam, Biden will have no excuse if he shows up unprepared.

It's hard to imagine Donald Trump behaving this way toward any of his own political rivals. His reflex has always been to defend his own political prerogatives at any cost, including the long-term interests of his party or nation.

Sanders seems to be prepared to make a different choice — one that recognizes how dramatically the political landscape has changed with his latest primary defeats, and how much his country's dire circumstances have eclipsed his own.

Barring a dramatic reversal in next week's contests in Arizona, Florida, Illinois and Ohio, he should bring his campaign in for a landing next week. With that single, pragmatic act, he can debunk the cynics' blithe assertion that all populists are alike. He can also show the world that Trump's divisive poison has been contained to one party — and that Sanders and his Democratic allies mean to arrest its spread.

Brian Dickerson is the Editorial Page Editor of the Free Press. Contact him at bdickerson@freepress.com.