This is a KFF Health News story.
On the campaign trail, both former President Donald Trump and Vice President Kamala Harris are eager to portray themselves as guardians of Medicare. Each presidential candidate accuses the other of backing spending cuts and other policies that would damage the health insurance program for older Americans.
But the election's outcome could alter the very nature of the nearly 60-year-old federal program. More than half of Medicare beneficiaries are already enrolled in plans, called Medicare Advantage, run by commercial insurers, and if Trump wins, that proportion is expected to grow -- perhaps dramatically.
Trump and many congressional Republicans have already taken steps to aggressively promote Medicare Advantage. And Project 2025, a political wish list produced by the conservative Heritage Foundation for the next presidency, calls for making insurer-run plans the default enrollment option for Medicare.
Such a change would effectively privatize the program, because people tend to stick with the plans they're initially enrolled in, health analysts say. Trump has repeatedly tried to distance himself from Project 2025, though the document's authors include numerous people who worked in his first administration.
Conservatives say Medicare beneficiaries are better off in the popular Advantage plans, which offer more benefits than the traditional, government-run program. Critics say increasing insurers' control of the program would trap consumers in health plans that are costlier to taxpayers and that can restrict their care, including by imposing onerous prior authorization requirements for some procedures.
"Traditional Medicare will wither on the vine," said Robert Berenson, a former official in the Jimmy Carter and Bill Clinton administrations who's now a senior fellow at the Urban Institute, a left-leaning research group.
The concept of letting private insurers run Medicare isn't new. Former House Speaker Newt Gingrich, a Republican, asserted in 1995 that traditional Medicare would fade away if its beneficiaries could pick between the original program and private plans.
The shift to Medicare Advantage was accelerated by legislation in 2003 that created Medicare's drug benefit and gave private health plans a far greater role in the program.
Lawmakers thought private insurers could better contain costs. Instead, the plans have cost more. In 2023, Medicare Advantage plans cost the government and taxpayers about 6% -- or $27 billion -- more than original Medicare, though some research shows they provide better care.
The Trump administration promoted Medicare Advantage in emails during the program's open enrollment period each year, but support for the privately run plans has become bipartisan as they have grown.
"It helps inject needed competition into a government-run program and has proven to be more popular with those who switch," said Roger Severino, lead architect of Project 2025's section on the Department of Health and Human Services (HHS). He served as director of HHS' civil rights office during the Trump administration.
But enrollees who want to switch back to traditional Medicare may not be able to. If they try to buy supplemental coverage for the 20% of costs Medicare doesn't cover, they may find they have to pay an unaffordable premium. Unless they enroll in the plans close to the time they first become eligible for Medicare, usually at age 65, insurers selling those supplemental plans can deny coverage or charge higher premiums because of preexisting conditions.
"More members of Congress are hearing from constituents who are horrified and realize they are trapped in these plans," said Andrea Ducas, vice president of health policy at the Center for American Progress, a liberal public policy organization.
Editor's note: This article was updated on Nov. 4, 2024, to correct the amount Medicare Advantage plans cost the government and taxpayers last year compared with the cost of original Medicare.