Former Vice President Joe Biden defended his reasoning to not legalize marijuana on a federal level if elected president, saying there is not "enough evidence" as to "whether or not it is a gateway drug."

Speaking at a town hall in Las Vegas on Saturday, the 2020 Democratic presidential candidate said whether the U.S. should legalize cannabis on a federal level is still up for debate as far as he is concerned.

"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," Biden said, according to Business Insider. "It's a debate, and I want a lot more before I legalize it nationally. I want to make sure we know a lot more about the science behind it."

Biden, as he has throughout his time on the campaign trail, said he supports medical marijuana and insisted possession of the substance "should not be a crime."

But he also said Saturday that he thinks the decision to legalize marijuana should be left up to individual states.

"States should be able to make a judgment to legalize marijuana," he said at the town hall.

As for legalization on a federal level, Biden said more research is needed.

"It is not irrational to do more scientific investigation 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," Biden said.

Several of his top Democratic rivals in the race have thrown their support behind legalizing marijuana, which is currently classified as a Schedule I substance, which the Drug Enforcement Administration defines as drugs "with no currently accepted medical use and a high potential for abuse." Other Schedule I drugs include heroin and LSD.

Biden's campaign previously noted the former vice president would reschedule the substance as a Schedule II drug to aid in researching its health impacts.

Sens. Cory Booker (D-N.J.), Elizabeth Warren (D-Mass.), and Bernie Sanders (I-Vt.) have all said they would make marijuana legal on a federal level if elected president.

Democratic presidential candidate Andrew Yang in a tweet Monday morning said he believes marijuana should be legal throughout the country, a position he has held since releasing a plan that would pardon individuals who are imprisoned for nonviolent marijuana convictions.

--This report was updated on Nov. 18 at 11:16 a.m.