Joe Biden is under fire from rivals for the Democrat presidential nomination after he said cannabis could be a “gateway drug”.

The former Vice President was asked about federal legalization of recreational marijuana at an event in Las Vegas at the weekend. He said there is not enough evidence on whether it is a gateway drug and he would demand a lot more evidence before deciding to legalize it.

Biden is a long-term opponent of adult-use marijuana legalization, and his comments drew criticism from his key political rivals. “Let’s be clear: marijuana isn’t a gateway drug and should be legalized,” said Kamala Harris, whose bill to decriminalize cannabis at a federal level, expunge non-violent marijuana possession convictions and compensate those disproportionately affected by the war on drugs will go before the House Judiciary Committee tomorrow.

Harris was once among the frontrunners to secure the Democratic nomination, but she has since lost momentum and she is now considered an outsider. Biden is second in the betting, behind favourite Elizabeth Warren and just ahead of Pete Buttigieg.

Sanders also hit back at Biden’s comments. He said that Americans are united on their desire to see adult-use marijuana legalized in every state, citing a poll conducted by Pew Research in September.

Sanders and Warren have both framed marijuana legalization as a matter of racial justice, as black communities have been disproportionately affected by prohibition. Regular polls show that legalization is popular among Americans that identify as Democrat supporters, so it is interesting to see Biden continuing to oppose it.

Fellow White House hopeful Andrew Yang said he believes the former Vice President’s views will evolve over time, while he reiterated the need to regulate marijuana consumption and make it safer for all Americans. Oregon Rep. Earl Blumenauer urged Biden to “get with the program” and added that it is time to end a senseless prohibition that has ruined countless lives. New York Rep. Alexandria Ocasio-Cortez also emphasized her support for legalization.

Author A. R. Moxon took a more biting tone when he said that Biden has his finger firmly on the pulse of 1994. Biden was a key proponent of tough criminal penalties for marijuana possession in the 1994 crime bill, and many critics have linked that to a significant rise in incarceration for marijuana offenses.