While she has publicly stated her support for single-payer health insurance, cosponsoring Sanders' bill is more of a formal step. Elizabeth Warren of Massachusetts, Kamala Harris of California and Kirsten Gillibrand of NY, are also supporting the bill, according to news reports.
Warren, Sanders, Harris, Booker, and Gillibrand are arguably the most famous and most-admired Democratic senators in the country among the party's base; the betting markets give a 63 percent chance that one of them will be the 2020 nominee for president. Sheldon Whitehouse is the latest lawmaker to announce plans to co-sponsor legislation to create a single-payer health system.
Democrats are also worrying over whether placating Sanders' far-left, anti-establishment supporters will alienate moderate Democrats to such a degree that it will be impossible to gain congressional majorities in 2018 and the presidency in 2020. In a single-payer structure the government pays all the medical bills.
Sen. Joe Manchin (D-WV) told Bloomberg that he was open to exploring a single-payer health insurance program.
Flagrantly progressive Sen. Elizabeth Warren (D-Mass.) threw in her support for the bill shortly after Harris. No Democrat would run for president, or even for House or Senate minority leader, without supporting the DREAM Act.More news: Tropical Storm Jose forms over the open Atlantic
More news: Reshuffle of Cabinet on Sunday, more exits imminent
More news: Turkey calls for end to violence in Myanmar
"You should not be punished because you are working class or poor...."
The Democratic push for a health care system that covers all Americans comes as Donald Trump and his Republican allies in Congress are moving in the opposite direction, trying but so far failing to repeal the Affordable Care Act.
And the way things are going, soon no Democratic leader will be able to oppose single-payer.
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".
Sen. Cory Booker of New Jersey on Monday became the latest to offer support for Sanders' legislation.
That's not to say single-payer isn't gaining support elsewhere in the Senate Democratic caucus. In the House, meanwhile, well over 100 Democrats have co-sponsored Rep. John Conyers' "Expanded & Improved Medicare For All bill".
The Vermont independent nearly stole the Democratic presidential nomination from Hillary Clinton a year ago.