"Make America Great Again" is shown to be first used by Alexander Wiley in the 76 US Congress in the 1940s. The concept behind the phrase was to encourage Americans to work together to improve the country's economy and infrastructure. In the years following Wiley's use of the phrase, it was adopted by both the Democratic and Republican party.
Bill and Hillary Clinton used the phrase during their presidential campaigns, as did Barry Goldwater during his run for the Republican nomination. Donald Trump announced his candidacy for President and chose "Make America Great Again" as his campaign slogan. Trump's use of the phrase caught on with his supporters and became a rallying cry for his campaign. Since Trump's election, the phrase has been used by other politicians to drum up support for their own agendas.