As President Trump’s foreign policy takes effect, anti-U.S. countries may feel the sting. For Colombia, that first taste has already come, and the results bode well for the future of American foreign policy in the hemisphere.

Colombia is one of the most historically conservative and U.S.-aligned countries in South America; indeed, it has been the largest recipient of U.S. foreign aid on the continent.

That all changed when President Gustavo Petro was elected in 2022 as part of a broader leftward shift in Latin America.

This shift was a big win for the global left. It allowed communist China to establish itself as South America’s leading trading and investment partner and enabled China’s state-owned firms to take control of the Panama Canal. It also gave leftist dictators in Cuba, Venezuela and Nicaragua new allies to expand their anti-U.S. alliance.

For four years, President Biden stood silently by as these regimes systematically eroded democratic freedoms, allowed cocaine and fentanyl production to soar and poison our people, promoted illegal migration, and embraced Iran and its proxies. U.S. influence in South America reached a new low.

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Although this was a victory for the left, it was a massive blow to Colombia, whose capitalist model Mr. Petro quickly transformed.

In his first address to the United Nations General Assembly, Mr. Petro railed against “coal and oil,” blaming them for “the climate disaster that will kill hundreds of millions of people.” He cut Colombia’s oil production—which the government relied on to pay for health, education and other public services—and the country’s economy backslid.

Yet even while cutting fossil fuel production in Colombia, Mr. Petro eagerly pursued agreements to purchase Venezuelan gas exports and help prop up the dictatorial regime.

He targeted Colombia’s pro-American security forces through demotions and funding cuts. This impaired their ability to check narco-guerrilla activity, resulting in historic levels of coca production.

In April 2023, Mr. Petro took his radical message directly to the American people, issuing an address at Stanford University posing climate as “the beginning of the extinction of humankind.” His solution? The world should “join together in a revolution against capital.”

Thankfully, the former M-19 Marxist guerrilla’s fortunes proved extraordinarily short-lived.

Colombians have resoundingly rejected Mr. Petro’s radical policies, leaving him with an approval rate of just 34%.

His administration has been plagued by corruption. His son was arrested on money laundering charges involving drug traffickers. His chief of staff and former campaign head resigned over allegations of illegal campaign funding from Colombian mafias tied to the Venezuelan government. Eventually, Mr. Petro’s congressional coalition fractured, leaving his ambitious leftist agenda in tatters.

Mr. Trump’s recent diplomatic victory over Mr. Petro further rubbed salt in the wounds.

When Mr. Petro attempted to refuse repatriation of Colombian migrants deported from the U.S., Mr. Trump retaliated with threats of tariffs and visa restrictions, saying Mr. Petro’s actions had jeopardized national safety.

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Mr. Petro’s domestic and foreign policy antics could cost Colombia its U.S. aid, which has totaled almost $4 billion over the past five years, with billions more paid out by the U.S.-funded World Bank and Inter-American Development Bank.

Mr. Trump has frozen all foreign aid programs pending a 90-day review of whether each program promotes U.S. interests. Mr. Petro’s destructive policies will surely bring aid to Colombia under scrutiny.

While Mr. Petro’s regime staggers, the broader Western Hemisphere is undergoing a remarkable ideological shift to the right.

Argentina, Paraguay and Ecuador have all recently elected pro-U.S. conservative leaders. Elections are coming soon in Chile, Canada and Colombia; all expect conservative victories.

With newly confirmed Secretary of State Marco Rubio (born to Cuban immigrants) at the helm, Mr. Trump has a historic opportunity to improve inter-American relationships based on shared values and interests.

Mr. Trump will seize this opportunity to scale back Latin America’s dependency on China, end its failed socialist experiments and usher in an era of inter-American peace and prosperity.