|World War I pillow cover as seen in the book, Sweetheart & Mother|
Pillows by Patricia Cummings
Churchwell traces the reference back further than Charles Lindbergh's use in the 1940s. She found that the Republicans first used it as a slogan in the 1880s. Then, in 1915, Woodrow Wilson mentioned the phrase while suggesting neutrality in World War I. Churchwell states that the words were then taken over by isolationists and later became a slogan of the Ku Klux Klan, whom, she says, tried to say they copyrighted it (not true).
Today, "America First" is a prominent slogan of President Donald J. Trump. It now seems to be a rallying call for nativist tendencies, decreased immigration practices, and going it alone in the world by imposing severe tariffs on other countries (sometimes at the expense of our own).
I am so thankful to Sarah Churchwell for clearing up the puzzle and to Smithsonian Magazine for excerpting that part of her book.