When President Barack Obama is trying to persuade Americans not to do something, he has a go-to line: “That’s not who we are.” Whether the issue involves discrimination, immigration, torture, criminal violence or health care, he invokes the nation’s very identity. And he likes to follow it by adding, “We are better than that.”

In this way, throughout his political career, Obama has embraced the American tradition of rugged individualism, while arguing that it has always been bound by “an enduring sense that we are in this together.” America, he says, is “sustained by the idea that I am my brother’s keeper and I am my sister’s keeper.”

Indeed, Obama’s constant emphasis on “who we are” is his most original contribution to presidential rhetoric. You can search in vain for anything quite like it in the speeches of the great 20th century presidential rhetoricians, Franklin Delano Roosevelt and Ronald Reagan. Nor did Obama’s immediate predecessors, Bill Clinton and George W. Bush, tend to speak in such terms.

Whether or not it’s deliberate, Obama is using a distinctive approach in social science, which often goes by the unlovely name of “identity salience.” The basic idea is that if you make some aspect of people’s identity salient -- if you make them think about who they are -- you can influence how they act.

A famous demonstration from 1999 involved undergraduate Asian-American women taking math tests. When the experimenters made the participants’ ethnic identity salient (by posing a series of questions about it), their scores jumped. But when the experimenters made the participants’ female identity salient, their math scores got worse.

Later studies have demonstrated that identity salience matters for other characteristics as well. If, for example, you give student-athletes a reminder that they are athletes, they will do less well on a math test.

Some of the more intriguing applications involve cooperation. If all members of a group are given a sense of shared identity (for example, as fellow students at one university), they will become more likely to cooperate with each other -- and less likely to follow their own narrow self-interest.

Leaders of all kinds, whether or not they read social science, are alert to the power of making certain abilities and characteristics salient. Angelo Dundee, perhaps the best boxing trainer of all time, had the difficult task of training Muhammed Ali, who did not exactly like to take direction. But Dundee had a brilliant trick: “Every now and then I’d subtly suggest some move or other,” he explained, “couching it as if it were something he was already doing.” For example: “‘My gosh, you threw a tremendous uppercut. That was beautiful!’ But he had never thrown an uppercut.”

Every human being has an assortment of diverse identities, and it greatly matters which one is triggered by social situations, which hold up different kinds of mirrors. The same is true for nations. The U.S. is committed to free enterprise, federalism, a limited government and a strong military -- commitments that have historically favored Republicans. The country is also committed to expanded civil rights, ladders of opportunity and a measure of redistribution -- commitments that have historically favored Democrats.

Donald Trump may not speak explicitly of “who we are,” but with his promise to make America great again, he engages in his own kind of identity politics, signaling that the nation has lost its sense of self. That gets to people. Hillary Clinton, as well, invoked national identity in the most impressive moments in her acceptance speech: “Our country’s motto is e pluribus unum: out of many, we are one. Will we stay true to that motto?”

Masterful politicians, and effective agents of change, tend to succeed by singling out, and making salient, some aspect of a nation’s self-understanding, sparking a sense of recognition -- and ultimately moving voters in their favor. Obama made it into an art form. Hillary Clinton is no artist, but her electoral prospects may well depend on whether she manages to steal some of his distinctive thunder.

By Cass R. Sunstein
Bloomberg

Cass R. Sunstein is a Bloomberg View columnist. He is the author of “The World According to Star Wars” and a coauthor of “Nudge: Improving Decisions About Health, Wealth and Happiness.” -- Ed.