Joe Biden has it, and so does Bernie Sanders. Donald Trump and Ben Carson have it, too -- at least, they seem to. But Hillary Rodham Clinton strains to achieve it. And Jeb Bush? He doesn't seem to want to try.
The elusive quality is authenticity, and it's become a preoccupation of the 2016 presidential campaign. Can candidates convince voters -- amid all the noise and artifice of politics -- that they are real people underneath, with character and convictions?
"Will you say anything to get elected?" CNN's Anderson Cooper asked Clinton at the first Democratic debate. But voters surely have the same question about Bush, and Marco Rubio, and everyone else who counts as a traditional politician.
When voters say they want authenticity, they often mean honesty and trustworthiness, for starters. We also want "straight talk," something Trump, Carson and Sanders all provide. We want candidates to open up and show some emotion, not just talking points written by campaign strategists.
What we want, in short, is a glimpse into a candidate's soul. Because that's not exactly easy to achieve -- even in a campaign that lasts almost two years -- we ask our candidates to jump through hoops. We demand a look at their families. We even expect them to appear on television and tell jokes, or sing or even (in the case of Sanders) dance with Ellen DeGeneres, to prove that they can be good sports amid indignity. If a politician is willing to embarrass himself publicly, we seem to believe, he's probably not a robot.
Here's the thing: The variety show routine isn't a reliable test of the qualities we're looking for.
"Often, what people respond to is how comfortable (the candidates) seem to be," Deborah Tannen, a Georgetown University linguist, told me last week. "But that often has nothing to do with honesty. If someone sounds stiff, or pauses to choose the right words, we sometimes think they must be cooking up a line. But they might just be inarticulate, or introverted, or worried about saying something the wrong way."
Put otherwise: Some candidates may be authentically robotic.
She cited an old joke from theater and broadcasting: "The key to success is sincerity. If you can fake that, you've got it made."
Moreover, Tannen warned, the mania for authenticity may disadvantage women.
"Women are expected to talk in ways that are incompatible with the ways we think a leader sounds," she said. "But if we think of displays of emotion as evidence of authenticity, they can easily be seen as too emotional. That's a huge double bind."
Most important, authenticity -- that is, the appearance of authenticity, since we can rarely be sure that what looks authentic is real -- probably isn't the right trait to value above all others.
"What does this have to do with whether a person can make good decisions?" Tannen asked.
Take the two most successful presidents of the last half-century, Ronald Reagan and Bill Clinton. Both were accused by their opponents of being inauthentic. Critics loved to point out that Reagan was a professional actor; Clinton's enemies called him "Slick Willie."
George W. Bush, on the other hand, won two elections partly because he excelled at authenticity; he was the candidate, famously, whom voters wanted to have a beer with. But that didn't make his presidency a success.
Likewise, Trump, Carson and Sanders have won high marks from voters for being blunt and plain-spoken, but that's not a reliable guide to whether they would be good at the job. It's only a starting point.
As Ted Cruz said at last week's debate, noting the widespread view that he's not the most likable of the GOP candidates: "If you want someone to grab a beer with, I may not be your guy. But if you want someone to drive you home, I will get the job done."
It's sensible to scrutinize the candidates' honesty and credibility, from Hillary Clinton's shifting statements about emails to Trump's indignant denials of things he said only a few weeks ago.
But it's time to stop chasing the elusive notion of authenticity. We don't really know how to measure it. And even if we did, it's the wrong measurement to use.
Contact Doyle McManus, columnist for the Los Angeles Times, at email@example.com