Most politicos would quickly realize that the slogan "Make America Great Again" was not new. Rather, both Ronald Reagan and George H.W. Bush had used a "Let's Make America Great Again" slogan ubiquitously in their campaigns in the 80's. Trump however, captured the slogan in a federal registration, and was able to do so because the original slogans had been abandoned. That is, the easiest way to lose rights in a mark is to stop using it with no intention to use it again, leaving it free for any third party to pick up.
Accordingly, the original intent-to-use application for "Make America Great Again" (Serial No. 85783371), which covered PAC services and political fundraising, was processed relatively smoothly. This application then became effective as a federal trademark registration on July 14, 2016, a month after Trump formally announced his campaign and met the "actual use in commerce" requirement of federal marks.
The protected slogan was immediately and aggressively enforced, and when GOP primary rivals Senator Cruz and Wisconsin Governor Walker began using the phrase "make America great again" in their speeches, Trump's army of attorneys quickly shot off cease-and-desist letters.
To bolster this protection, a series of additional applications (Serial Nos. 86724213, 86724115, 86716074) were sent off in August, 2015, and materialized into registrations throughout 2016. As a result, only Trump could then, legally, "Make America Great Again" during the election year, not only in PAC and fundraising speeches now, but also on trucker hats, bags, umbrellas, bumper stickers, baby and pet clothing, footwear, campaign buttons, online journals, social networking services, and more.
The iconic red cap had already made its way into the NY Times Style section on Fashion Week, dubbed as an "ironic summer accessory", and promptly sold out at the Midtown store in the Trump Tower. “How many did we sell? Does anyone know? Millions!” Trump said during the Washington Post interview.
Naturally, the now famous (or infamous) slogan had created a counterfeit market, but in Trump's own words "[i]t was knocked off by others. But it was a slogan, and every time somebody buys one, that's an advertisement." The campaign therefore "selectively" enforced their trademark rights, perhaps only pursuing a minimal amount of policing just to avoid claims of dilution (and possibly cancellation) of the mark, but assuredly prevented any political rivals from using the same.
Throughout the ups and downs of the tumultous Trump campaign, the message remained a certain and resonating constant.
"Make America Great Again".
As David Axelrod (Obama's chief political strategist) said during an interview, “[i]n terms of galvanizing the market that [Trump] was talking to,” Axelrod said, “he did it single-mindedly and ingeniously.”