[snopes.com]

"Despite their embrace of the slogan, however, there is no evidence that the Ku Klux Klan invented it, as has sometimes been alleged. There are instances of its use by politicians predating any examples we’ve found directly attributable to the Klan.

President Woodrow Wilson ran for re-election on an “America first” platform in 1916, for example, in that instance using the phrase to remind voters that his isolationist stance had kept U.S. troops out of the burgeoning conflict in Europe (nevermind that he abandoned that position and sent them to fight in World War I during his second term). A popular song called “America First!” was dedicated to Wilson and published in 1917.

For that matter, Presidents Calvin Coolidge, Warren G. Harding, and William McKinley all used the catchphrase at one time or another to promote isolationist and/or protectionist foreign policies (we found an instance of McKinley being touted as having an “America first” agenda as long ago as 1896)."