Hemp and marijuana are both types of Cannabis sativa, but they’re bred differently, and have different biological attributes. Most importantly, hemp does not have psychoactive properties, because it has far lower levels of tetrahydrocannabinol (THC) than marijuana. The two plants look different, too—hemp stalks are long, thin, and fibrous, while marijuana grows closer to the ground.

Still, for decades after hemp was criminalized, Congress wouldn’t touch it with a 10-foot pole. “Everybody said, ‘That’ll never happen! Everybody thinks that it’s pot, and nobody’s going to support it,’” said Senator Ron Wyden, a Democrat from Oregon who started the legalization push back in 2012.

Hemp’s multitude of uses include food, lotion, and (perhaps most profitably) a recently approved epilepsy drug called Epidiolex made of cannabidiol (CBD), a cannabinoid that can be extracted from cannabis in both its marijuana and hemp forms. It’s legal to sell products made from hemp in the United States, but the market is currently filled almost entirely by imports from other countries.

Around the same time Wyden introduced his first bill to legalize hemp, Kentucky state officials started to consider the crop as an alternative for farmers struggling to make profits on tobacco, which has historically been the state’s top agricultural commodity but whose importance has declined in recent years. In 2012, James Comer, then Kentucky’s agricultural commissioner and now a first-term congressional representative, made legalizing hemp under state law his top priority. Legalization passed the Kentucky legislature with bipartisan support, but was stalled by the state’s attorney general because of hemp’s federal status.

So Kentucky’s hemp advocates turned their attention to Congress. Legalizing hemp, they argued, could give Kentucky farmers a chance to corner the market and help make up for some of the tobacco losses.

In 2013, after hearing from officials and advocates for several months, Senator Mitch McConnell of Kentucky, the Senate majority leader, jumped on board with the proposition. That year, a bipartisan coalition of the two Republican senators from Kentucky—McConnell and Rand Paul—and the two Democratic senators from Oregon—Wyden and Jeff Merkley—introduced the first version of the Industrial Hemp Farming Act, which would have removed hemp from the controlled-substances list and made it legal to grow as an agricultural commodity.

They weren’t successful, in large part because hemp’s continued association with pot made it too much of a political liability. But with the Senate’s top Republican publicly arguing that hemp wasn’t marijuana and shouldn’t be treated as such, members of both parties began to sign on to the Senate version of the bill.

At McConnell’s urging, the 2014 farm bill created the pilot research program that authorized universities and state departments of agriculture to grow and research hemp. Because hemp was still a controlled substance, there were many restrictions on its cultivation—farmers who wanted to participate in the program had to get a waiver from the Drug Enforcement Administration, and the number of acres farmers could legally plant was strictly limited. But, according to a congressional report, at least 19 states participated in the pilot program, and at least 40 have since passed legislation relating to the cultivation of industrial hemp. “I’m one of hemp’s biggest advocates, and I never expected it to go this fast,” said Jonathan Miller, a former Kentucky state official who is the general counsel, the spokesperson, and a registered lobbyist for the U.S. Hemp Roundtable.