Most of the poll-leading Democrats running for president have said they support nationwide legalization of marijuana for recreational use.

The exception atop the polls: former Vice President Joe Biden.

He has proposed decriminalizing marijuana use and automatically expunging previous convictions. He also supports the use of cannabis for medical purposes and reclassifying it so the federal government can study its impact.

“Biden believes no one should be in jail because of cannabis use,” his campaign’s criminal justice policy says.

But Biden falls short of calling for the nationwide legalization of recreational marijuana. He proposes leaving that decision to the states.

On Wednesday, Illinois becomes the 11th state to broadly legalize marijuana’s sale and use.

Biden came under fire from some of his fellow candidates when, during a November town hall event in Las Vegas, he suggested more study is needed to determine whether marijuana is a gateway to use of other drugs. He later told reporters that he was saying some in the medical community feel more research is needed.

According to the National Institute on Drug Abuse, some research suggests marijuana use is likely to precede use of other legal and illegal drugs. However, the majority of individuals who use marijuana do not go on to use “harder” substances, according to the institute.

“There are serious medical folks who say we should study it more,” Biden said in a late November conference call with reporters, according to a transcription by the Nevada Independent news site. “There’s enough serious scientists who say let’s give us a little more chance to actually study it. And that’s what I’ve said. But I don’t think it’s a gateway drug. There’s no evidence I’ve seen that suggests that.”

Most of the other front-running Democratic candidates have supported the full, nationwide legalization of recreational marijuana and the expungement of past pot convictions.

South Bend, Ind., Mayor and presidential candidate Pete Buttigieg — who has been leading recent polls in Iowa — supports both.

So, too, do U.S. Sens. and presidential candidates Elizabeth Warren and Bernie Sanders.

Sanders said he would use executive action to start the process of legalizing marijuana, which ultimately would require an act of Congress.

Warren, like many of the candidates who speak on the topic, note the disproportionate impact of marijuana convictions on minorities, especially black Americans.

“Right now in this country, the best evidence suggests that African-Americans and whites use marijuana at about the same rates, and yet African-Americans are far more likely to be arrested for marijuana use than whites are,” Warren said during a CNN town hall in April. “So every time we start to talk about criminal justice reform, for example, I think a good place to start is with the things we make illegal, and one of the best places we could start is by legalizing marijuana.”

Cory Booker, a presidential candidate and U.S. senator from New Jersey, introduced legislation that would legalize recreational marijuana nationwide and expunge previous convictions.

“I believe we have meaningfully shifted the conversation on marijuana policy in this country,” Booker wrote in July in his response to an American Civil Liberties Union’s candidate questionnaire.

New York entrepreneur and presidential candidate Andrew Yang pushed back at Biden’s suggestion that states should decide whether they want to legalize recreational marijuana.

Yang supports legalization and the expungement of convictions.

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“(Yang) thinks that putting people in jail for something that is legal in other parts of the country is stupid, has been applied in an unequal manner that has unfairly targeted and disadvantaged black and brown kids, and we should instead focus on taxing and regulating marijuana,” a Yang campaign spokesman said.