The current top income tax rate is 37 percent, which makes Ocasio-Cortez’s proposal seem radical. But she rightfully pointed out that, as recently as the 1970s, top tax rates were in the 70s.

Doing things just because we’ve done them in the past is a bad rationale for policy, but there’s an actual economic rationale behind a 70 percent top tax rate. And it comes from something called “optimal tax theory.”

It starts with the simple premise that we should tax people to optimize the well-being of all citizens. And ultimately that requires takes money from people who don’t need it (the rich) and giving it to those who do (the poor) — and continuing to do so until it’s counterproductive.

So when MIT’s Peter Diamond and UC Berkeley’s Emmanuel Saez explored this question in a 2012 paper, they came up with a top tax rate that would optimize welfare: 73 percent.

This video explores the idea of optimal tax theory using … potatoes.

To watch more Vox videos, follow us on YouTube. And we will be sure to follow up with more potatosplainers.

But things are changing. Historians and native activists are questioning Columbus’s legacy. Cities like Columbus, Ohio, are opting out of celebrating Columbus Day, and others like Denver, Colorado, are celebrating Indigenous Peoples’ Day instead.

The Columbus myth is built on some notable omissions. Educational videos like this one teach children that Columbus defied conventional wisdom and proved the world was round. In fact, most people at the time already knew the world was round. Columbus claimed that it was smaller than predicted, and he was wrong.

But arguably the most egregious myth is that Columbus “discovered” America, and did so peacefully. Not only where the islands he first landed on in 1492 inhabited by the Taíno people, but the arrival of Columbus and his men ushered in an era of enslavement, disease, and destruction that resulted in mass deaths of the native people on the island.

With this record, it’s hard not to wonder how Columbus became an American hero memorialized in statues and the names of cities and streets, and even a holiday complete with parades.

The answer begins during the Revolutionary War. As the US fought the British for their independence, they needed a heroic symbol, and Columbus fit the bill. He was a rebellious, non-British sailor who had left Europe for the Americas in search of opportunity.

Over the years, streets and cities were named after him. Biographies like Washington Irving’s “The First Voyages of Columbus” further cemented his glorified tales of discovery. But it was when Italian immigrants started arriving in the US in large numbers in the late 1800s that the myth of Columbus really took off.

Italians were facing harsh discrimination, which was only made worse by their Catholic beliefs. So just like the US when it was fighting for independence, Italian immigrants, bolstered by the Catholic organization Knights of Columbus, found a mythological hero to rally behind. And who better than Columbus? He was Italian, Catholic, and already admired.

Watch this video to understand how Columbus became an American icon, and why his legacy is controversial.