Senator Bernie Sanders Jason Merritt/Getty Images Bernie Sanders is getting some serious support in his push to reform the US healthcare system.

Sanders on Wednesday will roll out a Medicare-for-all bill, which aims to extend the Medicare program, federally funded insurance for people over the age of 65, to all Americans.

A single-payer healthcare push has previously been well outside the mainstream for most Democrats. But Sanders' legislation has picked up support from high-profile Democrats.

The latest Democratic senator offering support is Kirsten Gillibrand of New York.

"Health care is a right, not a privilege," Gillibrand tweeted Tuesday. "This week, I'll proudly join Senator @BernieSanders to co-sponsor Medicare for All."

Sen. Cory Booker of New Jersey also offered support for Sanders' legislation this week.

"I'm signing onto Medicare-for-all, which I'm excited to do this week," Booker said in an interview with NJTV on Monday. "Sen. Sanders, myself, and some others are going to be announcing some legislation this week along with some of my other colleagues."

Booker, who has been floated as a possible contender for the Democratic presidential nomination in 2020, said Obamacare was just a "first step" in securing healthcare for all Americans.

"What we have right now is a country where just because of your wealth, it will depend on whether you have healthcare or not," Booker continued. "You should not be punished because you are working-class or poor and be denied healthcare. I think healthcare should be a right to all."

Booker's announcement comes after other high-profile Democrats said they would cosponsor the bill.

Sen. Kamala Harris, who also has been floated as a 2020 contender, said at a town hall late last month that she would also co-sponsor the bill.

"This is about understanding, again, that healthcare should be a right, not a privilege. And it's also about being smart," Harris said.

Sen. Elizabeth Warren, another senator popular with the progressive wing of the Democratic Party, announced her support on Thursday in an email to supporters.

"I believe it’s time to take a step back and ask: what is the best way to deliver high quality, low cost health care to all Americans?" Warren wrote. "Everything should be on the table — and that’s why I’m co-sponsoring Bernie Sanders’ Medicare for All bill that will be introduced later this month."

The movement on Sanders bill comes as single-payer healthcare has become much more popular among the American public in polling. Even business titans like Warren Buffett have backed the idea.

The bill still faces almost impossible odds of passage, given that Republicans control Congress and the White House. But Sanders' move signals it will be a policy fight Democrats are willing to pick for the foreseeable future.

Sanders, along with the cosponsors, will roll out the legislation at a large event featuring doctors, hospital workers, and more on Wednesday.