Bogota, Sept. 1 -- The United States chose a theatrical moment to flex its gatekeeping power. On the margins of United Nations week in New York, Washington revoked the visa of Colombia's President Gustavo Petro, citing "reckless and incendiary" conduct after he addressed a pro-Palestinian crowd and urged American soldiers to refuse unlawful orders. Petro answered with defiance, calling the step an affront to international norms and a warning to smaller nations that the host country intends to police who may speak in the global commons. In a capital that prizes propriety, the spectacle landed like a dare.

Petro's response was immediate and unbowed. On social media and to reporters, he framed the decision as proof that Washington prefers p...