President Harry Truman signs the Marshall Plan on April 3, 1948 in Washington. The plan played a key role in the reconstruction of Europe after World War II and was part of the wide-ranging moves by the U.S. to establish a new international order that still defines the world to this day. AFP/Getty Images hide caption
From the ashes of World War II, President Harry Truman presided over the creation of global institutions that have defined the international order for the past 80 years.
"It must be a policy of the United States to support free peoples who are resisting attempted subjugation by armed minorities or by outside pressure," Truman said as he spelled out his doctrine in a 1947 speech to Congress.
In a few short years, the U.S. helped establish and lead the United Nations, NATO, the World Bank and the International Monetary Fund. The U.S. helped rebuild Europe with assistance funneled through the Marshall Plan, and also funded the reconstruction of Japan.
Democratic and Republican presidents supported these institutions for generations. They sometimes grumbled at the cost, yet believed they ultimately strengthened the U.S. as the world's leading superpower.
But 100 days into his second term, Donald Trump is moving aggressively to scale back the U.S.'s role in the world, based on his "America First" agenda. Trump sees this web of alliances, treaties and soft power as expensive, outdated relics that restrain America's ability to act decisively on its own.
"I'm not aligned with anybody. I'm aligned with the United States of America, and for the good of the world," Trump said in February.
Trump says the U.S. should not be the world's policeman and should not guarantee the security of its allies. Rather, he has attacked many of them and threatened to take control of territory ranging from Greenland to Canada to the Panama Canal to the Gaza Strip.
Hal Brands, a historian at the American Enterprise Institute, a conservative Washington think tank, puts it this way: "If I had to boil it all down, I would say Trump's goal is to extract more privileges from the international order while bearing fewer responsibilities for upholding them."
Trump scaled back U.S. global commitments in his first term. In his second term, he's launched a much more ambitious effort.
"In the first term, I would say the defining characteristic of this foreign policy was chaos. This time he's really taking a sledgehammer approach to U.S. foreign policy and the institutions around it," said Kelly Grieco with the Stimson Center, a nonpartisan think tank.
Trump wants to do this on all major fronts - military, diplomatic and economic.
President Trump and Ukraine's President Volodymyr Zelenskyy held a contentious meeting at the White House on Feb. 28 over the Russia-Ukraine war. Trump opposes additional U.S. military aid to Ukraine, though the two countries on Wednesday signed an agreement to share future revenue from Ukraine's natural resources. SAUL LOEB/AFP via Getty Images hide caption
With the U.S. military, Trump wants to end U.S. involvement in open-ended wars, like the Russia-Ukraine conflict.
His signature moment so far was the White House meeting two months ago where Trump and Vice President Vance berated Volodymyr Zelenskyy, saying the Ukrainian president had not shown enough gratitude for U.S. aid and was overestimating Ukraine's military capabilities.
"You're not in a good position. You don't have the cards right now," an agitated Trump said to Zelenskyy. "You're gambling with the lives of millions of people. You're gambling with World War III."
The president opposes further U.S. military assistance for Ukraine and wants a permanent ceasefire. However, this is proving elusive as the fighting grinds on, with Russian leader Vladimir Putin launching some of its largest aerial assaults of the war in recent weeks.
"He's underestimating, often,