... in which he asked for exclusive rights to use “Make America Great Again” for “political action committee services, namely, promoting public awareness of political issues and fundraising in the field of politics.” He enclosed a $325 registration fee....
The slogan itself was not entirely original. Ronald Reagan and George H.W. Bush had used “Let’s Make America Great Again” in their 1980 campaign — a fact that Trump maintained he did not know until about a year ago.
“But he didn’t trademark it,” Trump said of Reagan.
His decision to claim legal ownership reflected a businessman’s mind-set. “I think I’m somebody that understands marketing,” Trump said....
The trademark became effective on July 14, 2015, a month after Trump formally announced his campaign and met the legal requirement that he was actually using it for the purposes spelled out in his application.
January 19, 2017
Trump thought of the line "Make America Great Again" the day after Mitt Romney lost the 2012 election.
"Five days later, Trump signed an application with the U.S. Patent and Trademark Office..."