At the center of his foreign policy vision,
Trump started using the slogan in the later months of his campaign, and despite requests from the Anti-Defamation League that he drop it, he stuck with it.
Friday, he embraced the words as a unifying theme for his inaugural address.
"From this day forward, a new vision will govern our land," Trump said on the Capitol steps. "From this day forward, it's going to be only America First. America First."
Those same words galvanized a mass populist movement against U.S. entry into the war in Europe, even as the German army rolled through France and Belgium in the spring of 1940.
A broad-based coalition of politicians and business leaders on the right and left came together as the America First Committee to oppose President Franklin D. Roosevelt's support for France and Great Britain. The movement grew to more than 800,000 members.
While the America First Committee attracted a wide array of support, the movement was marred by anti-Semitic and pro-fascist rhetoric. Its highest profile spokesman, Charles Lindbergh, blamed American Jews for pushing the country into war.
"The British and the Jewish races," he said at a rally in September 1941, "for reasons which are not American, wish to involve us in the war."
The "greatest danger" Jews posed to the U.S. "lies in their large ownership and influence in our motion pictures, our press, our radio, and our government," Lindbergh said.
It is unclear if Trump is bothered by the ugly history of the phrase. What is clear is that he is determined to make the words his own. He has used them to sell his promises to impose trade barriers, keep manufacturing jobs inside the U.S. and restrict illegal and legal immigration.
"Every decision on trade, on taxes, on immigration, on foreign affairs, will be made to benefit American workers and American families," Trump said in Friday's inaugural speech.
"We must protect our borders from the ravages of other countries making our products, stealing our companies, and destroying our jobs," he said.
"It is such a toxic phrase with such a putrid history," said Susan Dunn, professor of humanities at Williams College and an expert in American political history, in an interview.
Lindbergh and other prominent members of the America First organization believed democracy was in decline and that fascism represented a new future, Dunn said.
Those words "carry an enormous weight," said Lynne Olson, author of "Those Angry Days," a book about the clash between Lindbergh and Roosevelt over entering the war.
"That time was strikingly familiar to now," Olson said. "There was an enormous amount of economic and social turmoil in the country, anti-Semitism rose dramatically as well as general nativism and populism."
Shortly after Trump took the oath of office, White House aides posted a 500-word description of Trump's approach to the world titled "America First Foreign Policy."
"The world must know that we do not go abroad in search of enemies, that we are always happy when old enemies become friends, and when old friends become allies," the statement read. It added that defeating radical Islamic terror groups will be the "highest priority," and that Trump's administration would add ships to the Navy and build the Air Force back up to Cold War levels.
Trump also plans to withdraw from the Trans-Pacific Partnership and renegotiate the terms of
Trump appears to have first tried out the phrase "America First" during an interview with the New York Times in March, when he was asked if he was taking an isolationist, "America First" approach to foreign policy.
"Not isolationist, I'm not isolationist, but I am 'America First.' So I like the expression. I'm 'America First,'" Trump said at the time. "We have been disrespected, mocked and ripped off for many, many years by people that were smarter, shrewder, tougher," he added.