Perhaps you can understand why Cory Booker finds Pete Buttigieg’s success as a candidate a little frustrating. As the New Jersey senator has pointed out, like Buttigieg, he was a Rhodes scholar and a mayor (though of Newark, a city nearly three times as large as South Bend, Ind.). Yet Buttigieg has gotten loads of positive media coverage and has seen his stock rise, with at least one poll putting him first in Iowa.

So a pro-Booker super PAC has decided to air an ad in Iowa directly targeting Buttigieg:

One might reasonably ask why a political action committee trying to help a trailing candidate is going after the guy who’s currently in fourth place in national polls. Whatever the strategic calculation, there are a lot of people in the Democratic Party who resent Buttigieg’s (still modest) success and would like to see him taken down a peg or two.

Do they have a point?

The simplest answer is: Sure. Buttigieg is 37 years old. He’s the mayor of a city of approximately 100,000 people, which makes it the 306th largest city in the United States. On the most basic level, it’s ridiculous to think you could go from that job right to being president.

Booker isn’t the only one who has found Buttigieg’s success exasperating. Last month, Sen. Amy Klobuchar (D-Minn.) argued that a female candidate of Buttigieg’s age and résumé would never be taken seriously. “Do I think that we would be standing on that stage if we had the experience that he had? No, I don’t,” she said of herself and the other female candidates. “Maybe we’re held to a different standard.”

It’s difficult to argue with Klobuchar. In fact, it’s difficult to imagine a 37-year-old female mayor of a mid-size city even considering a run for governor, let alone president. Buttigieg has benefited from a particular kind of bias shared by the media and many voters: When we think “president,” we imagine a white guy, and so even an extremely young white guy seems plausible enough to take seriously.

In all likelihood, Buttigieg decided to run for president because there were no more proximate rungs on his ladder. He can’t run for Congress because his district is heavily Republican. (In 2016, Donald Trump beat Hillary Clinton there by 23 points). Becoming governor of Indiana is similarly unlikely. And, these days, even an unsuccessful run for president can give your career a boost; heck, Housing and Urban Development Secretary Ben Carson wound up with a Cabinet position in an area he had never spent even a moment contemplating.

And Buttigieg is unquestionably talented. He may not be Barack Obama, but he’s smart, articulate and personable. If you like former vice president Joe Biden’s ideological and political approach, but would prefer someone less than half his age, Buttigieg is your guy.

Experience isn’t everything, of course; there have been good and bad presidents who brought experience to the job. But being a successful president does require a unique combination of knowledge, character, vision and temperament. They have to wrangle Congress to pass a legislative agenda, manage the world’s largest organization with more than 4 million employees and a budget of more than $4 trillion, navigate complex relationships with other countries, and deal with natural and human-caused crises.

If nothing else, it’s easier for voters to determine whether someone can do all those things when they can look at what that person did in jobs of increasing responsibility that dealt with the types of domestic and foreign issues a president is responsible for. Since there’s no other job quite like that of president, voters will always be guessing at how a person might perform, but at least the candidate’s history can provide some clues. With Buttigieg, there really isn’t that much to go on.

It’s not all that surprising that Buttigieg would be the target of ire (spoken or otherwise) from some of his opponents. Every candidate who isn’t winning will inevitably believe there’s something unjust at work in a race that isn’t rewarding them for the fact that, in their own minds, they’re the obvious choice. To run for president, you need an enormous ego and tons of self-confidence, so all of them probably feel that if voters would just listen, they’d be in the lead — or at the very least where Buttigieg is, not leading but in a position to get there.

But Buttigieg is particularly likely to frustrate other candidates. If you’re behind Biden you can say, okay, that makes some sense: He’s been around forever, he was vice president, he’s obviously qualified. You might look at Sen. Bernie Sanders (I-Vt.) and say, I get it, he’s got a base of support on the left that won’t desert him no matter what. But a pipsqueak like Buttigieg? What’s he got that I haven’t got?

In the end, the answer may be: Not enough, at least not this time around (after all, he could run 10 more times before he’s too old). But if he keeps gaining strength, other candidates both above and below will be only too eager to try to take him out.

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