What’s more, Buttigieg receives the sort of scrutiny one might expect from a front-runner despite being way behind in national polls. Joe Biden represents the far greater threat to the young left’s favored candidate, Bernie Sanders. But Biden seems to avoid much of the highly personal animosity heaped on his co-runner in the competitive lane of B-Surnamed Moderates.

What’s going on here? Let’s begin with the most straightforward explanation.

1. Don’t overthink it: They hate him because he’s not a socialist—and his early-state poll numbers are rising.

This is the obvious answer and, frankly, it might be the only answer. In the past two months, no candidate has gained more than Buttigieg in the early states. If he wins in Iowa and New Hampshire, he could block Bernie Sanders’s path to the nomination. And this deeply concerns young progressive activists, who rightly see the Democratic primary as a zero-sum competition to lead the party in a winnable election that has the potential to redefine the Democratic platform for a decade or longer. Buttigieg, far more than Biden, has the youth and vigor to command the party for the next generation. And this makes him the graver threat to those arguing for a socialist revolution.

This explanation takes us pretty far. But I’m not sure it quite captures the level of sulfuric hate in the progressive objections to his candidacy.

2. Keep not overthinking it: They also hate him because they think he’s a liar.

There’s no question that Buttigieg, glimpsing an opening in the moderate lane, has tacked toward the center in the past few months. He initially seemed to support Medicare For All, and now he openly criticizes the effect it would have on private-insurance employment. He initially proposed radical government reforms such as packing the Supreme Court and removing the filibuster, but now he’s recast himself as a moderate unifier. As a result, the left sees him as not just any moderate, but as a moderate masquerading as a wunderkind grassroots progressive. When my colleague Elaine Godfrey spoke with a Sanders supporter in North Carolina, he told her that Buttigieg “threatens to put a fresh face on the most nakedly cynical underbelly of the post-triangulation Democratic Party.” For the young left, political moderation might be a misdemeanor; but eloquent moderation donning the costume of progressive activism is first-degree phoniness that merits the punishment of crude criticism.

3. Overthink it a little bit: Young people hate him because he’s a traitor to his generation.

Generational identity is arguably the most important dividing line in the Democratic Party—more than class, race, or education. As I’ve written, the young left has become a kind of third party awkwardly domiciled within the Democratic Party. Buttigieg, however, is a traitor to his generation; he is a 30-something Millennial who appeals mostly to middle-aged and older white voters.