When Christine Lo left her job in June, she was hoping Obamacare would mean she could still have health insurance.

Lo, 35, was confronted by a confusing enrollment process, which she said resulted in persistent calls from insurers trying to lure her in. Although she knew she would face tax penalties if she didn’t get coverage, she chose to cancel doctors’ appointments and go uninsured until she found a new job.

“I’m going to focus on finding a job that lets me have health insurance right away to avoid the whole Obamacare thing,” said Lo, who works in film and TV in New York.

Lo’s frustrations come as Barack Obama prepares to depart the White House and leave his legacy healthcare reform, officially known as the Affordable Care Act (ACA), in the hands of a new president.

The Republican nominee, Donald Trump, has said he will scrap Obamacare altogether on day one while the Democratic nominee, Hillary Clinton, is expected to try and rescue the health law as it enters a new, and worrying, stage in its development.

By many measures the ACA has been a tremendous success. Some 20 million more people now have insurance thanks to the ACA; people under the age of 26, who often skip insurance, can be covered by their parents’ plans; and people with existing conditions cannot be discriminated against. But the ACA relies on competition between insurers to provide affordable coverage, and that is dwindling.

Under the ACA, health insurance marketplaces, also called health exchanges, were set up to facilitate the purchase of health insurance in each state. Customers are free to choose from a set of standardized healthcare plans from participating insurers, and those policies are eligible for federal subsidies.

But insurers have been fleeing the exchanges, arguing that they are loss makers and the types of people attracted to them make the risks too great for the insurers to provide affordable (and profitable) policies.

David Howard, an associate professor at Emory University’s department of health policy and management, said the ACA included provisions to keep the marketplaces stable, but some of those were watered down in the push to get the deal through Congress, and in other cases the provisions have not been enacted in the way people expected. “So that means the exchanges are potentially on the cusp of falling apart,” Howard said.

The marketplaces are unstable in part because they are new, and all the parties involved – from insurers to those who need insurance – are trying to figure out where they fit into the equation. The system needs healthy people to enroll to help offset the costs of sicker people, but that is not what is happening – there are fewer enrollees than projected, and they are sicker than anticipated.

On top of that, premiums are expected to rise, which makes insurance from the marketplaces less attractive to the healthy, young people they need. “They’re eventually going to get to the point where premiums go up, healthy people drop out of the market, which causes premiums to go up more, then more healthy people drop out of the market, and eventually the whole thing just falls apart,” said Howard.

But others argue this period of instability, while a problem, is a natural - and temporary – part of the cycle.

Zack Cooper, an assistant professor of health policy and of economics at Yale University, said the markets are not stable now, but they should be in 10 years. “New markets take a while to get right, and these markets are different from the past,” said Cooper.

Obamacare was enacted in March 2010 and is still not fully implemented. Its growth has been hampered in part by partisan gridlock that has further undermined the exchanges.

“They haven’t changed the law since it was passed, and it was passed in a very convoluted, rushed state,” said Gerard Anderson, a professor of health policy and management at Johns Hopkins Bloomberg School of Public Health. “Normally, what you would have had was a whole series of technical changes over the last six years to make the law better, but they haven’t been able to do it.”

But major insurers have not shown interest in waiting for the markets to be sorted out. In April, UnitedHealthcare left most of the 34 state marketplaces it participated in. And in August, Aetna scaled back its participation in the markets because of losses, and also because of the justice department’s attempt to block it from merging with another health insurance giant, Humana.

These departures are weighing on the system because they reduce competition, a cornerstone of the health insurance marketplace. This is a problem in places like Pinal County, Arizona – which may soon be left without any options at all in the insurance marketplace.

“The marketplaces and the level of competition and number of issuers in some rural areas, regardless of who is president, is going to be something that rises up pretty high on their radar,” said John Graves, an assistant professor at Vanderbilt University School of Medicine.

It is estimated that 31% of US counties will have only one insurer in 2017, according to a Kaiser Family Foundation analysis released in April, up from 7% the year before.

But the ability to address these problems is, as Obama has experienced over the past six years, conditional on Congress.

“The state of the law is going to depend a fair bit on who wins and the degree to which Congress says, ‘OK, we passed this law, maybe some of us didn’t support it, but when something becomes law, we ought to collectively get together and say, now that’s it here, how do we make it as functional for our constituents as we can,’” Cooper said. “As opposed to using it as a tool to club your political opponents at the expense of people living in your district.”