"Like Paul Wellstone, I've always believed that health care is a right for all Americans -- not a privilege -- and that every person in our country deserves access to the care they need," Franken wrote on Facebook. "Establishing a single-payer system would be one way to achieve universal coverage, and Senator Sanders' "Medicare for All" bill lays down an important marker to help us reach that goal."
Sanders is set to introduce his legislation, which Democrats are calling "Medicare for All," on Wednesday. It would replace private health insurance markets and have the federal government foot all medical bills.
Already, two Democrats seen as potential presidential contenders, California Sen. Kamala Harris
and Massachusetts Sen. Elizabeth Warren, have said they'll co-sponsor the bill -- as have Rhode Island Sen. Sheldon Whitehouse, Hawaii Sen. Brian Schatz
and Massachusetts Sen. Ed Markey
. Sens. Kirsten Gillibrand of New York, Cory Booker of New Jersey and Jeff Merkley of Oregon all said they'll back the bill as well.
Booker also said he'll join them, revealing Monday that he will co-sponsor the bill in an interview with NJTV
. "I'm signing onto Medicare-for-all, which I'm excited to do this week," Booker said.
"You should not be punished because you are working-class or poor and be denied health care. I think health care should be a right to all," Booker said in the interview. "This is something that's got to happen. Obamacare was a first step in advancing this country, but I won't rest until every American has a basic security that comes with having access to affordable health care."
In a statement, Merkley said, "Health care should be a right for every single American, not a privilege reserved for the healthy and the wealthy."
He said moving to a single-payer program would "simplify health care and lower patients' costs."
Their support reflects the Democratic Party's growing embrace of a proposal that, even during the 2016 campaign, was seen as politically improbable. It also shows that lawmakers considering running for president in 2020 are eager not to look too moderate or cautious on an issue that excites the party's base.
Other senators are still expected to join the list of co-sponsors before Sanders unveils his bill Wednesday.
Connecticut Sen. Chris Murphy, meanwhile, is working on an alternative that would allow Americans to buy into Medicare -- an idea similar to the "public option" that many progressives unsuccessfully pushed for in the Affordable Care Act.
This story has been updated.