Joe Biden's opposition to pot has apparently gone up in smoke. The 2020 Democratic presidential candidate and former vice president on Monday rolled back his stance that marijuana is a "gateway drug" — and wrongly claimed that he had never said so in the first place.

"I don't think it is a gateway drug. There's no evidence I've seen to suggest that," Biden said in a conference call with reporters.

Biden claimed that he never said marijuana was a gateway drug, only that "some say" it is. When asked about legalizing weed, Biden said "some in the medical community" say pot needs to be studied more to determine whether it is a gateway drug or could be harmful when combined with other substances.

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But Biden said marijuana should be "totally decriminalized," and that anyone convicted for using the drug should have their criminal record "wiped totally clean, completely clean."

Biden caught fire from other Democratic contenders earlier this month after saying at a Las Vegas town hall that, if elected, he would not support legalizing marijuana because there has "not nearly been enough evidence" about "whether or not it is a gateway drug" that could lead to more harmful substances.

New Jersey Senator Cory Booker dug into Biden's remark at the Democratic debate November 20, telling the former vice president, "I thought you might have been high when you said it."

WATCH: @JoeBiden on marijuana legalization - "There is not nearly been enough evidence...as to whether or not it is a gateway drug," he said last night, "It’s a debate." Biden said states should decide on legalization & that he supports medical marijuana. @CBSNews pic.twitter.com/s4CE32phLS — Bo Erickson CBS (@BoKnowsNews) November 17, 2019

As vice president, Biden was a blunt opponent of marijuana. He told ABC News in 2010, "I still believe it's a gateway drug," and said legalizing it would be "a mistake."

Scientific research shows that smoking marijuana can be correlated with using other drugs and the development of addictions, but not enough to blame pot for a "gateway" effect. The National Institute of Drug Abuse says that marijuana can likely precede other drug use, but "the majority of people who use marijuana" do not go on to use harder drugs. The institute also says that any gateway effect from marijuana can also be tied to alcohol and nicotine.

Most of the Democratic presidential candidates support decriminalizing and legalizing marijuana. Booker introduced the Marijuana Justice Act in February, which seeks to end federal prohibition of the drug and expunge federal convictions for its use and possession. Four other presidential hopefuls in the Senate — Michael Bennet of Colorado, Elizabeth Warren of Massachusetts, Kamala Harris of California and Bernie Sanders of Vermont — co-sponsored the legislation.