Perhaps the most recognizable piece of political swag in recent history is President Donald Trump’s ‘Make America Great Again’ hat. The iconic red cap, which retails for $25, has sold out multiple times and won symbol of the year from the Stanford Symbolic Systems Program.

Trump submitted his application to trademark the phrase “Make America Great Again” back in November of 2012. He has profited from the decision politically and financially ever since.

The phrase is not original. Ronald Reagan and George H.W. Bush both said, “Let’s make America great again” in the presidential election of 1980.

Bill Clinton used the phrase in his 1991 presidential announcement speech but more recently referred to it as a “racist dog whistle.”

In the 2016 primaries, candidates Senator Ted Cruz and Governor Scott Walker used the phrase until the Trump operation sent cease-and-desist letters. His trademark allowed him to control his opponents and develop exclusive merchandise, most notably in hat form.

The majority of the MAGA caps are made in the Cali-Fame factory in Southern California by immigrant labor. The Washington Post estimates that Trump makes about $8 in profit for every hat sold (84,000 of them by June of 2016 for a total of $672,000).

Knock-off hats are made in factories in countries like Bangladesh, Vietnam and China. These manufacturers benefit greatly from demand, while Trump benefits from their reproduction because they help foster political support.

And, since Trump’s election, political merchandise has played a central role in protest culture.

At the Women’s March on January 21st, thousands of woman wore pink knit hats with distinctive ears as a way for “women, whether transgender or cisgender,” to “come together to support women’s rights in a creative and impactful way.” The hats were controversial in certain circles but undeniably popular.

One major difference between the pink and red hats is who they benefit. Unlike Trumps’ red hats, the pink hats are usually handmade. No one company or individual profits. However, a rise in pink yarn sales has benefited companies like Michael’s as well as local knitting stores.

Furthermore, the careers of founders Krista Suh and Jayne Zweiman are likely to benefit from their idea taking off.

The safety pin trend began after the Brexit referendum: Wearing a safety pin came to symbolize solidarity with those who are victims of hate crimes. After the election, the trend crossed the pond. Celebrities like Kerry Washington are still wearing them.

While a regular old safety pin can seem easy to find, many craft stores started selling out after the election, and some entrepreneurial types have chosen to capitalize on the demand for them as statement jewelry. Etsy artist Rebecca Cullen achieved notoriety for marketing a $335 safety pin necklace.

Other artists have created their own more affordable versions and pledged to donate proceeds to charity.

Not all political merch becomes a viral success.

As the Democratic candidate for President, Secretary Hillary Clinton also sold a wide range of products including shirts designed by fashion heavyweights like Michael Kors, Tory Burch, Diane von Furstenberg and Joseph Altuzarra. She even sold “woman cards” for $5 a pop.

Jeb Bush was the center of many jokes after he tried to sell a $75 “Guaca Bowle” on his campaign site.

Rand Paul hawked branded products including a spy cam blocker and a beer mug featuring a picture of a dog holding an American flag under the word, “UNLEASH.” Of his merch, he said, “Thomas Jefferson would be proud.”

But none of these products crossed over into the mainstream.

There are many reasons people purchase political merchandise. Tom Davis, Associate Director of the Symbolic Systems Program at Stanford University, explains that “red and pink hats are ways for their wearers to identify themselves with a political movement. The hats promote the movement, or advertise it, to those who see them, and the hats signal to other people who identify with the movement that they are connected to each other.

“Plus they may keep your head warm or the sun off your face.”

No matter the reason for the demand, these symbolic goods are for sale everywhere from Amazon to Walmart. Turns out, running a campaign or a social movement, like running a large company, requires successful and widespread merchandising.