Former Vice President Joe Biden has been receiving widespread blowback from his Democratic primary rivals since voicing his support for a federal ban on recreational marijuana.

While speaking at a town hall event on Saturday, Biden said that while he believes that states “should be able to make a judgment to legalize marijuana” and even supports the use of marijuana for medicinal purposes, his opposition to recreational marijuana use “hasn’t changed.”

“The truth of the matter is, there’s not nearly been enough evidence that has been acquired as to whether or not it is a gateway drug. It’s a debate, and I want a lot more before I legalize it nationally,” Biden told a crowd of his supporters. “I want to make sure we know a lot more about the science behind it.”

“It’s not irrational to do more scientific investigations to determine, which we have not done significantly enough, whether or not there are any things that relate to whether it’s a gateway drug or not,” he continued. “I don’t know enough to know whether it is.”

While the Democratic frontrunner is not the sole presidential hopeful calling to keep marijuana illegal under federal law, he has been receiving criticism from his primary challengers for the position.

Sen. Kamala Harris (D-CA), who oversaw the prosecution of nearly 2,000 marijuana convictions while serving as San Francisco’s District Attorney, has recently flipped her stance on legalization of the drug and even joked about smoking while she was a student at Howard University.

“Let’s be clear: marijuana isn’t a gateway drug and should be legalized,” Harris responded to Biden. “Glad to see my bill with Rep. [Jerry] Nadler take the next step in the House this week.”

Let's be clear: marijuana isn't a gateway drug and should be legalized. Glad to see my bill with Rep. Nadler take the next step in the House this week. https://t.co/d6BcMFlpYT — Kamala Harris (@KamalaHarris) November 18, 2019

Accordingly, the California lawmaker introduced legislation into the Senate in July which would not only decriminalize and deschedule marijuana, but also provide for reinvestment into certain individuals who have been convicted of drug crimes.

Sen. Bernie Sanders (I-VT), a longtime advocate of marijuana legalization, also scolded Biden for his opposition.

“The American people are united on issue after issue,” Sanders said. “We must legalize marijuana now — and expunge all past marijuana convictions as a matter of racial and economic justice.”

The American people are united on issue after issue. We must legalize marijuana now—and expunge all past marijuana convictions as a matter of racial and economic justice. https://t.co/NQjp7WOko3 — Bernie Sanders (@SenSanders) November 17, 2019

Less than a month ago, the self-styled democratic socialist unveiled a sweeping proposal where he would use his executive power as president of the United States to both federally legalize the drug and expunge related criminal convictions. Sanders argues that the law disproportionately targets minorities and “ruined the lives of millions of Americans,” as reported by The Washington Post.

Entrepreneur Andrew Yang also echoed similar sentiments, calling to resolve the ambiguity and legalize marijuana at the federal level.

“Marijuana should be legal nationwide,” Yang said. “It is already legal in several states, it reflects a safer approach to pain relief than opiates, and our administration of drug laws is deeply uneven and racist.”

Marijuana should be legal nationwide. It is already legal in several states, it reflects a safer approach to pain relief than opiates, and our administration of drug laws is deeply uneven and racist. https://t.co/0Uhl17MW98 — Andrew Yang🧢 (@AndrewYang) November 18, 2019

Yang has previously stated that legalization would not only improve safety and social equity, but would also generate tens of billions of dollars in new revenue based on legal cannabis businesses.