Days after the Stoneman Douglas High School massacre in February, Senator Marco Rubio appeared at a CNN town hall in Florida to discuss the shooting. One clip from the evening went explosively viral, featuring a question from survivor Cameron Kasky: “Senator Rubio, can you tell me right now that you will not accept a single donation from the NRA?” Rubio, looking aggrieved in his Sopranos-dark suit, replied, “So number one, the position I hold is the Second Amendment.”

Somebody in the audience began to yell at him, and he cut the shouter off. “No, number two, the answer to the question is that”—he gestured at himself and smiled—“is that people buy into my agenda.”

Buy into. The phrase is a fascinating one. It seems to have originated in Adam Smith’s The Wealth of Nations, when he notes that people, “to provide for a remote futurity,” rarely “buy into” long-term investments, especially in times of political uncertainty, even though these investments appear to be of equal or greater worth than short-term annuities. The phrase virtually never appeared again, except in specialist stock-market texts, until the 1980s, when it became a metaphor—at first, largely a negative one, meant to reveal the whimsy and illogic that drives our consumer choices: “People buy Nike shoes because they have bought into Michael Jordan ... not necessarily because of the quality of the shoes,” the business strategist John Maxwell wrote. “Why do you need to be physically beautiful?” the actress Colette Brown asked. “If we are judged on modern physical beauty then 90 percent of us are going to fail ... Fight the stereotype. Don’t buy into it.”

By this decade, though, it had largely become a positive metaphor: a necessary thing to sell a product or a political stance; even an indicator of the rightness or goodness of an idea. “The success of [welfare] depends on whether caseworkers and clients buy into the ideology of the institution,” a sociologist writes in Selling Welfare Reform. A self-help book tells us that “buying or purchasing items can be understood as a metaphor for accepting uplifting beliefs about the self or circumstances ... consider ‘buying into’ thoughts and ideas to improve yourself, [such as] ‘I buy into the principle that abundant finances are good for me.’” A government official told The New York Times that the only way to make political change is to first gauge “the public buy-in” for reforms.

How did we make this shift, as a society, from a suspicion of what people “buy into” to a hailing of it, a reverence towards it? I think it’s not a coincidence that the idea of “buy-in” and, in fact, the intrusion of economic language into many non-financial realms of life (“to invest in a relationship,” “to buy time,” “to have values,” “the marketplace of ideas”) gained sharp momentum in the 80s. The 80s, of course, were the Gordon Gecko decade, a “morning in America” overtly driven by the pumping-up of Wall Street. But I want to glance at the ’70s, the real progenitor of the 80s.

The 70s, of course, were defined by Jimmy Carter’s “malaise.” That malaise wasn’t only cultural: the 70s, fundamentally, conveyed to Americans that the power they thought they possessed after the Second World War to effect happy endings, to control the destiny of their own country and the world, had been lost. The noble overthrow of a corrupt president didn’t really matter: Vietnam had still been lost, OPEC could twitch an eyelid and Americans would sit for hours in gas-station queues, the Federal Reserve couldn’t keep up. An American-led coup d’etat in Iran in 1953 yielded, some 25 years later, a counter-revolution and the seizing of an entire American embassy’s worth of hostages.

If a fundamental belief in American goodness and effectiveness and power—the belief inherent in Marco Rubio’s “number one” answer to Kasky’s question, the enduring usability of the Constitution—could no longer be sustained, what could take its place? A belief in the market! A belief in the market as a kind of god: an impartial arbiter whose dictates we could believe in.

It’s interesting to me that the reasons that many early American leaders distrusted the market are the same reasons they distrusted pure democracy. The market—while necessary in a free society—seemed to capture the fearsome whims of the mob, its irrationality, herd nature, and susceptibility to demagoguery in the form of advertising and P.R.

And here we are, led by a president who not only specializes in demagoguery, but is obsessed with asserting his own popularity. Politically, we seem to have no real way, now, of asserting the value of a proposition—to defend it to the hilt—except for noting that it’s popular. That it’s prevailed in the “marketplace of ideas.” This situation extends to other fields beyond the political. Recently, discussing a book idea with an editor, he told me that the book’s artistic merit—not its salability—“comes down to this: Can we get 10,000 people to invest in your idea?” I felt confused: I’m not sure I need people to “invest in my idea,” I just want them to read it.

Of course, we know, deep down, that just because lots of people support an idea doesn’t mean it’s right. It can have been sold to them, as a certain interpretation of the Second Amendment has been sold. And just because lots of people support an idea doesn’t mean, as Adam Smith noted, that they are doing what’s most reasonable, nor even that their personal reasons are clear-cut. Many of the N.R.A.’s five million members, who are recruited through expensive television ads, may well join for symbolic reasons, or to be part of a community, not because they avidly support the organization’s core principles per se.

After the town hall, Rubio defended himself further on Twitter: “Banning all semi-auto weapons may have been popular with the audience at #CNNTownHall, but it is a position well outside the mainstream,” he insisted. Whether or not that’s true—and I doubt it is—many things, like voting rights for women and the equality of men with “different” skin colors (such as Rubio), were once outside the “mainstream,” and defended by people with vision and courage who did not base their beliefs on approval in the public-opinion marketplace.

The notion of “buy-in” as the barometer of what’s good and right is, I think, dangerously driving certain of the most confounding oddities in our contemporary politics. The irrepressible liberal obsession with “understanding” Trump voters—which has created its own tiresome media genre, the parachute-in article from the most benighted place in America filled with “real Trump voters”—arises from the desperate hope that if only these political adversaries can be properly “understood” or “empathized with,” then they can be made, like Nike shoe buyers converted to Adidas, to “buy into” Hillary Clinton or Bernie Sanders. That would make the world, to the left, comprehensible, instead of peopled by a whole bunch of voters whose consumer choices on the political marketplace appear not only incomprehensible, but, more importantly, reprehensible.

At the same time, the right-wing’s obsession with conspiracy theories—that the Parkland high-schoolers were actually paid by shadowy entities to weep and wail in favor of gun control, that Barack Obama is not really American, that many leaders are secretly huge lizards who take off their masks at night before dining together on human limbs—serve the same purpose. They prevent the right from having to face the fact that a lot of human beings, in fact the majority of Americans, have simply come to opposing views; that the political “market” may rule not in their favor; and that they may have to base their views on something other than their palatability to many perfectly ordinary Americans.

Marco Rubio’s response to Cameron Kasky’s question was not only emotionally inadequate—it was a total leadership failure. If Rubio intends to continue to support a lack of regulation for semi-automatic weapons in America, then he needs to come up with a powerful, real reason for that—not outsource the reasoning to the evidence of “buy-in.” He has chosen political life in order to lead, not only to serve.

The entire town hall exchange was heartbreaking. After Kasky asked his question, the crowd rose, grinned, and burst into wild claps. The camera panned back to Kasky. Unexpectedly, for a modern American political debate, Kasky didn’t look pleased at this show of public approbation. His face remained as it had been before: a rictus of pain and pale, deep bewilderment. That’s because Kasky had, tragically, been forced to come to the understanding of a moral principle far deeper than any he could learn by watching how people around him respond. His argument would have been the same, the viewer sensed, if he and Rubio had been sitting together alone, without the crowd. I’d ask whether Rubio’s would have been, too.