Sen. Cory Booker earned one of the biggest laughs of the fifth Democratic debate on Wednesday when he cracked a pot joke at Joe Biden‘s expense.

“This week I hear him literally say that I don’t think we should legalize marijuana. I thought you might have been high when you said it,” Booker quipped.

Although the joke lightened the debate’s mood for a moment, the exchange highlighted how far opinion on marijuana legalization has shifted over the last few years. A majority of Americans now say that marijuana should be “legalized” — which, as Booker advocates, would permit people to buy, sell and use marijuana. Biden has instead advocated for “decriminalizing” marijuana.

Legalizing marijuana would lift all legal prohibitions on the drug, while decriminalizing pot means that it would still be illegal — although people who break the law would face lesser penalties. For Biden, that would mean letting states legalize recreational marijuana; legalizing medical marijuana and banning jail time for marijuana use.

Just 20 years ago, only about 31% of Americans supported legalizing marijuana. Over the past two decades, more Americans have begun to use marijuana, and fewer are seeing it as harmful. Marijuana’s critics long said that it can have a “gateway effect” and can lead users to try harder drugs. Back in 2014, Biden himself described it as a “gateway drug.” However, experts say that there isn’t strong evidence that the effects of marijuana actually cause users to try other illegal drugs.

About 67% of Americans said that marijuana should be made legal, according to a Pew poll conducted in September — including 78% of Americans who are Democrats or lean Democratic. Booker has advocated for completely legalizing marijuana, arguing during the debate that the drug is “already legal for privileged people,” while people of color are disproportionately the target of law enforcement.

The push to legalize marijuana has also been supported by advocates for criminal justice reform, who say that marijuana arrests have contributed to mass incarceration. The ACLU noted in a 2013 report that while black and white people use marijuana at similar rates, black people are about 3.73 times more likely to be arrested for marijuana possession.

The comment also highlighted a very real divide between Booker and Biden’s generations. While 65% of members of Generation X — which includes Booker — support legalizing pot, legalizing marijuana is supported by only 35% of members of the Silent Generation, which includes Biden, according to the Pew poll. Millennials supporters, meanwhile, outnumber both groups, with 76% of that generation supporting legalization.

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