President Donald Trump’s “America First” foreign policy aims to put the nation’s economic and political interests ahead of other countries and global concerns like the environment.

But according to retired Gen. Stanley McChrystal, the former Commander of U.S. and NATO coalition forces in Afghanistan, U.S. leadership would be wise to consider how other countries may perceive such a policy.

McChrystal, speaking Monday at Fortune’s Brainstorm Tech conference in Aspen, Colo., said that while preaching an “America First” ideology may sound good to some, it can have an adverse affect on other nations that may feel threatened by the policy’s isolationist-tone.

“The reality is when you make ‘America First’ a bumper sticker and pump it overseas, what you’re telling them is ‘America Only,’” said McChrystal.

Although the typical Americans may not be well versed in the political affairs of India and Latin American countries, it’s likely those countries’ citizens know what is happening in the United States, he said.

“That’s not a bad thing, but that’s something we need to understand,” said McChrystal, who now works for the consulting firm he founded, the McChrystal Group. “How we present ourselves matters a lot, and that’s every American, not just at the senior levels.”

“If we want to be members of the world community, we need to think that way,” McChrystal continued.

Among the qualities of what makes good leaders, McChrystal said that they need be “smart, inspirational, honest,” but that to some extent, “everyone is flawed.” While leaders may not be perfect, good leaders can instill a feeling of trust in people, who believe that they are doing their best.

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When McChrystal was asked whether he considered President Trump to be a good leader, the retired general joked, “I don’t think his hair would have passed my command’s standards.” He didn’t directly answer the question, but he said that everyone must “look at the president of the United States through [their] own lens.”

“We got to be empathetic for the person who is sitting or standing in that office and make our own judgments,” he said.