“During his first term, from 2017 to 2021, Trump withdrew the US from multiple international agreements, including the Joint Comprehensive Plan of Action (JCPOA), often called the Iran deal. That agreement, negotiated in 2015 under President Barack Obama, essentially eased US sanctions on Iran in exchange for curtailing its nuclear program and allowing greater international oversight of it.
“The Iran deal was one of the worst and most one-sided transactions the United States has ever entered into,” Trump said when the agreement was terminated in 2018. Since then, Iran has built up its stockpile of enriched uranium and increased its missile supply, reportedly bringing the program much closer to developing nuclear capabilities — despite the Trump administration’s promise that Iran would never have them.
Trump also pulled the US out of the Paris climate agreement, which commits all signatories to reducing greenhouse gas emissions. Other diplomatic casualties of the Trump administration include the Intermediate-Range Nuclear Forces Treaty (INF), a Cold War-era pact between the US and Russia limiting the development of short- and intermediate-range nuclear weapons; the Open Skies Treaty, which allows signatories to conduct military reconnaissance flyovers; and two international migration agreements.
Trump also repeatedly critiqued NATO during his first term. He argued the other countries in the military alliance weren’t spending enough on defense (and they did begin to spend more), questioned whether the organization was still necessary, and in 2020 withdrew almost 10,000 troops stationed in Germany, a decision Vice President Kamala Harris’s foreign policy adviser Philip Gordon said seemed “designed to send a message about the limit of what Americans are prepared to spend to defend foreign borders and, more broadly, uphold world order.””
https://www.vox.com/2024-elections/382679/trump-foreign-policy-america-first-tariffs-nato-alliance