New York Sen. Kirsten Gillibrand is the latest Democrat to declare her support for Bernie Sanders’ upcoming “Medicare for all” health care proposal. She shared her intent to co-sponsor the legislation, which Sanders is expected to propose on Wednesday, via Twitter:

Health care is a right, not a privilege. This week, I’ll proudly join Senator @BernieSanders to co-sponsor Medicare for All. — Kirsten Gillibrand (@SenGillibrand) September 12, 2017

Gillibrand is the latest in a slew of Democrats to co-sponsor Sanders’ plan, alongside Sens. Elizabeth Warren, D-Mass., Kamala Harris, D-Calif., and Cory Booker, D-N.J. Many point out that those who have expressed support for the legislation are considered contenders for the 2020 presidential race.

One prominent Democrat, however, refuses to support the bill: House Minority Leader Nancy Pelosi said Tuesday that she wouldn’t back Sanders’ legislation, noting that she was instead focused on “protecting the Affordable Care Act.”

“None of these things, whether it’s Bernie’s [plan] or others’, can really prevail unless we protect the Affordable Care Act,” she said.

Pelosi disputed the idea that supporting single-payer health care is turning into a “litmus test” for the Democratic Party: “I think to support the idea that it captures is that we want to have as many people as possible, everybody, covered, and I think that’s something that we all embrace.”

But, as noted in a piece by Dylan Matthews on Vox, Democrats may not be able to ignore the support for Medicare for all much longer:

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. The rest of the party is getting on board with single-payer — or “Medicare for all,” where the federal government would provide health insurance for every American financed through taxes — as well. 117 House Democrats (over 60 percent of the caucus) have co-sponsored HR 676, the Expanded & Improved Medicare For All Act offered every Congress by Rep. John Conyers (D-MI). This is what an emerging party consensus looks like. Over time, some issues become so widely accepted within a party as to be a de facto requirement for anyone aspiring to lead it. No Democrat would run for president, or even for House or Senate minority leader, without supporting the DREAM Act. No Republican would try for a leadership position without supporting repeal of the estate tax. And the way things are going, soon no Democratic leader will be able to oppose single-payer.

Recent polls show that a majority of Americans support a single-payer system—a trend that is “the logical conclusion of recent health-insurance trends,” according to Catherine Rampell of The Washington Post. But despite this rising support for single-payer health care, dozens of Democrats have yet to voice support for Sanders’ legislation.