While some states have legalized pot, it remains illegal on the federal level.
"It's a state and a federal issue. The federal issue is that we should remove marijuana from the Controlled Substance Act. That's a federal decision," Sanders told CNN. "The state decision is that we live in a federal system of government where issues like tobacco and alcohol are significantly regulated by the states. And I think that is a province of the states."
The bill is a long-shot in the Senate and Sanders declined to say whether he had any co-sponsors for the measure. But Sanders and others say it would allow growers and dispensers in states where marijuana is already legal to use the banks.
The proposal plays to his base of younger and more liberal supporters, who have helped build his campaign into one that packs arenas and has mobilized the grassroots. That momentum has been slipping recently, with the latest polling finding Clinton even retaking the lead in New Hampshire.
Sanders only recently staked out a clear position on marijuana, promising last week in a campaign speech that he would seek to place the decision with states. But he has been inching toward the proposal in recent weeks.
During the October 13 CNN/Facebook sponsored Democratic debate he said would vote in favor of a Nevada referendum
to legalize marijuana. And he said Tuesday that he supported the Ohio referendum to legalize marijuana, though voters ultimately weighed in against it
"The state wants to go forward, they should be able to go forward without legal impediments from the federal government, and that's what this legislation is about," Sanders said. "Colorado wants to legalize marijuana, it's their decision. If Alabama does not want to legalize marijuana, that's their decision. But if a state wants to go forward, it should be able to do so without impediments from the federal government, which now prevent stores that sell marijuana from using banks, because that's in violation of federal law."
Though Sanders proposal comes on the heels of the Ohio vote against legalizing pot, pro-marijuana activists say the Ohio measure split their community because of the way it licensed growers.
"A growing majority of Americans want states to be able to enact their own marijuana laws without harassment from the DEA, and lawmakers should listen," said Tom Angell, founder of Marijuana Majority and a veteran marijuana activist in a statement. "The introduction of this bill proves that the defeat of the Ohio marijuana monopoly measure that wasn't widely supported in our movement isn't doing anything to slow down our national momentum."
Supporters of a similar House measure introduced last year said that Sanders' office began reaching out to them a few weeks ago to ask about filing a similar measure in the Senate.
"We're thrilled, and we hope it picks up additional co-sponsors and momentum in the Senate," said Rep. Jared Polis, a Colorado Democrat and the longtime sponsor of the House measure to decriminalize marijuana.