As politics metastasizes through all parts of American life, it seems as though everything must become subordinate to ideology. The latest casualty is kindness.

Recently, television talk-show host Ellen DeGeneres − a political progressive and noted activist for LGBTQ rights − was captured on video at a Dallas Cowboys football game, yukking it up and obviously having a great time with conservative former president George W. Bush. On social media, all hell predictably broke loose as people − including many high-profile progressives − criticized her for, essentially, consorting with the enemy. In response, she defended their friendship on her talk show.

DeGeneres finished with this statement: "When I say, 'Be kind to one another,' I don't mean only the people that think the same way that you do. I mean be kind to everyone."

Some applauded this, saying we need more of these sorts of courageous friendships in our troubled political times. Personally, I didn't think the friendship was so miraculous; I defy anybody to spend time with our 43rd president and not like him personally. And while I do not know DeGeneres, I strongly suspect the same could be said about her.

Amazingly, however, many denounced her statement as foolish, naive and perhaps even dangerous. For a famous activist to place kindness above political outrage neutralizes her effectiveness, right? Wrong. DeGeneres is more powerful and effective as a leader precisely because of her kindness. In healing division, she not only improves the world but also is more persuasive to others.

Don't believe it? Let's look at one typical research finding. In 2015, researchers at Georgetown University and the Grenoble School of Management in France conducted a large-scale workplace study that asked the question: "Being nice may bring you friends, but does it help or harm you in your career?" To find out, they examined the effect of being nice and civil in the workplace on three specific work outcomes: being sought out for advice, being perceived as a leader and job performance.

Those who practiced kindness came out ahead in all three categories. And the better performance reviews weren't just a matter of a supervisor's perception: The employees actually performed better because they were nice. It turns out that by being nice, employees "increase the likelihood that others seek − and presumably exchange − information and advice, which, in turn, increase performance."

But there's more. The Georgetown-Grenoble researchers also concluded: "Rather than hurting themselves by appearing weak or deferential, behaving respectfully seems to garner influence . . . For leaders and potential leaders, civility appears to be very valuable − it elicits warmth, allowing for an initial connection or relationship to take root; yet it also signals the ability to lead."

In other words: Ellen 1, Critics 0.

Former president Barack Obama, the most successful liberal politician in modern memory, is clearly of the DeGeneres school of thought. At the Oct. 25 funeral of Elijah E. Cummings, the late Democratic congressman from Maryland, Obama said: "I tell my daughters ... being a strong man includes being kind. That there's nothing weak about kindness and compassion."

I met Obama only once, in 2015 for a public conversation on poverty at Georgetown University, in front of a large audience. We disagreed very strongly on policy, but he was kind and generous to me.

The Democratic candidates vying for the presidential nomination might want to take note of Obama's words instead of taking every opportunity to show contempt for the people and ideas with which they disagree. Politicians on both sides should listen, in fact. A Republican member of Congress recently told me that he feels anguished because, to stay in office, he often has to be a person he didn't admire. He has to say harsh and unkind things, he said, even though he wants to be friendly and tolerant. Activists on his own side, who would accuse him of being a sellout and weak, had backed him into a corner.

I understood his conundrum, particularly in today's rancorous political environment. But I reject the premise that to win, one must be a jerk. There is no inconsistency between kindness and effective, winning leadership. This does not make me an idealist; it just means I am paying attention to the best social science.

Is being kind to those with whom we strongly disagree difficult? Of course it is. It requires self-control and maturity, like anything else that is worthwhile. It requires us to act like the people we want to be, not the way we feel at any given moment. It means seeing ourselves in others and actively practicing gratitude. But with commitment and repetition, we can become kinder people, leaders admired by others and a greater force for good in a troubled world.

Arthur C. Brooks is a professor of public leadership at the Harvard Kennedy School, senior fellow at the Harvard Business School and author of the bestseller, "Love Your Enemies."