Former South Bend, Ind., mayor Pete Buttigieg is the youngest Democratic presidential candidate; Sen. Bernie Sanders (I-Vt.) is the oldest (roughly double Buttigieg’s age). Buttigieg consistently demonstrates a mature understanding of how one unites a party and builds a winning general-election coalition. Sanders seems clueless.

Appearing at a Fox News town hall on Sunday, Buttigieg told the audience that “we can send a message to people who are telling us that we have to choose between our head and our heart, that we have to choose between what it takes to govern and what it takes to win, or that we have to choose between unity and boldness in this country." While he has defended himself against attacks from Sen. Elizabeth Warren (D-Mass.) and against the argument that he lacks age and maturity, Buttigieg has rarely gone negative on any opponent. That is extraordinary in a primary as close and competitive as this one. He understands at the end of the process, the bare minimum he must do is unite the party before turning to every persuadable voter.

The polar opposite of this is Sanders and his fleet of Bernie Bros who slash and burn, attack and smear other Democrats. The New York Times reports on Sanders’s swarm of online supporters, who have waged vicious and personal attacks on his critics, often focusing on feminist women. “Some progressive activists who declined to back Mr. Sanders have begun traveling with private security after incurring online harassment. Several well-known feminist writers said they had received death threats,” the Times explains. “A state party chairwoman changed her phone number. A Portland lawyer saw her business rating tumble on an online review site after tussling with Sanders supporters on Twitter.”

While he might perfunctorily chide his followers, Sanders hired one of social media’s most aggressive trolls, David Sirota. Sanders cannot possibly mean to control the divisive rhetoric and animosity spewing from his camp while hiring people infamous for such conduct.

Sanders’s denials often strike one as implausible. When a printed, detailed script attacking Warren surfaced and was circulated in multiple states, Sanders shrugged it off as if some low-level employee could have independently drafted and distributed the attack guide. If you have even a passing familiarity with presidential campaigns, as one former staffer from another camp told me, you know some volunteer or low-level staffer in Sioux City, Iowa, is not generating this stuff.

Sanders’s own behavior sets the tone and belies the notion that he is not responsible for the most divisive campaign in the primary. His team’s baseless claim (for which he had to apologize) that former vice president Joe Biden is corrupt was positively Trumpian. The out-of-context clip that Sanders distributed on social media falsely suggesting Biden favored Social Security cuts was slapped down by fact-checkers, but Sanders continued to insist that Biden supported cuts.

Sanders’s holier-than-thou ethos often manifests itself in refusal to answer ordinary, utterly appropriate questions. When asked how much his extravagant plans cost, he insisted, “You don’t know, nobody knows, this is impossible.” The Trump camp must be licking its chops, waiting for a candidate who thinks it is beneath him to answer such essential queries.

Sanders’s campaign, like all primary campaigns, is a preview of the general-election race and, if elected, the administration he would lead. A nominee who insists on personally attacking all doubters and the media might be a model for the Republican Party, but Democrats are not going to win with their own Donald Trump, especially one who has burned bridges and stirred resentment in his own party.

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