Sen. Bernie Sanders of Vermont has next to no chance of overtaking Hillary Clinton to win the Democratic presidential nomination, but he is having a profound impact in shaping Clinton’s campaign positions -- especially on health care.

Clinton, the former secretary of state and New York senator, has been adamant in her support of the Affordable Care act and has dismissed Sanders’s call for a new “single-payer” national program that would guarantee all Americans health care as too costly and impractical.

Related: How Obamacare Could Backfire on Hillary Clinton

But Clinton on Monday suggested during a campaign stop in Virginia that she would be open to allowing some people under the age of 65 to buy into Medicare, the premier federal health care plan for seniors.

Seniors are obliged to pay premiums to receive health care coverage, but the vast majority of the cost of physician treatment, hospitalization and drugs is picked up by the federal government.

“I’m also in favor of what’s called the public option, so that people can buy into Medicare at a certain age,” Clinton said, according to a report by Bloomberg News.

Sanders has argued that while the Affordable Care Act is a good start in expanding the availability of health care insurance, it still leaves tens of millions of Americans uninsured. He has described his pricey national health care proposal as “Medicare for all,” in effect providing Medicare-quality health care coverage to all Americans, regardless of their age or income levels.

According to the Bloomberg report, Clinton suggested that younger Americans, “people 55 or 50 and up,” could voluntarily pay to join the program.

Related: Get Ready for Huge Obamacare Premium Hikes in 2017

Clinton made those comments after coming under mounting pressure on health care reform not only from Sanders, her long-shot rival for the Democratic nomination, but also from some Democratic members of Congress, rank and file Democrats and health care professionals who say she should be more open to changes to address major shortcomings in Obamacare, as The Fiscal Times reported last week.

More than 2,000 physicians announced their support for a single-payer national health care system last week similar to Sanders’ call for “Medicare for all.” Those doctors complained in an editorial and paper published in the American Journal of Public Health about “persistent shortcomings” in the current health insurance system that threatens to leave millions of people uninsured indefinitely.

At the same time, many top doctors and surgeons have dropped out of Medicare because of low payments. And the Kaiser Family Foundation reports that 20 percent of primary care doctors are not accepting any new Medicare patients.

Clinton has long said that she was open to changes and improvements in Obamacare – and she has offered a number of proposals for expanding health care coverage and lowering the price of prescription drugs. However, she has been highly critical of Sanders for seeking a multi-trillion-dollar national health care plan financed by major tax increases. She has said she was reluctant to reopen the health care debate on Capitol Hill and give Republicans an opportunity to undermine or derail Obamacare.

Sanders, who defeated Clinton on Tuesday in their latest primary contest in West Virginia, said that while Clinton’s latest health care proposal was progress, it still fell well short of what was needed, according to The New York Times.

“Secretary Clinton’s proposal to let the American people buy into Medicare is a step in the right direction, but just like her support for a $12 minimum wage, it is not good enough,” Sanders said in a statement that described her idea as “Medicare for some.”

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