The nation's uninsured rate tumbled further last year, hitting the lowest rate on record, according to new government data that underscored what is at stake in the Republican effort to repeal the Affordable Care Act.
In the first nine months of 2016, just 8.8% of Americans lacked health coverage, survey data from the federal Centers for Disease Control and Prevention show.
That was down from 16% in 2010, when President Obama signed the healthcare law, often called Obamacare.
California, which has expanded Medicaid (known as Medi-Cal in the state) and created its own insurance marketplace through the law, has seen some of the most dramatic insurance gains with the share of uninsured residents dropping by more than half between 2013 and 2016, to 7.1%, data show.
"From expanding Medi-Cal to launching a competitive state-based marketplace, California is empowering consumers and providing quality and value," said Peter V. Lee, chief executive of the state's Covered California marketplace.
President Trump and GOP congressional leaders have pledged to roll back the law and replace it with something that will provide Americans with more affordable healthcare options.
On Tuesday, House Republican leaders repeated their pledges. "We will have a stable transition, where no one has the rug pulled out from under them while we work toward a better, more stable system," House Speaker Paul D. Ryan (R-Wis.) told reporters at the Capitol.
But Republicans are struggling to develop an alternative, even as growing numbers of Americans express concern about the repeal campaign.
And to date, neither the Trump administration nor Republicans in Congress have detailed how they plan to preserve the health protections that millions have gained through the current law.
The new report released Tuesday — which is based on surveys of more than 73,000 people's health insurance nationally — indicates that about 20.4 million people have gained coverage since 2010.
The most dramatic declines began after the law's system of coverage expansion began in 2014.
That year, states were able to access federal aid through the law to expand their Medicaid programs to cover more very low-income residents.
To date, 31 states have taken advantage of the Medicaid expansion.
The new data indicate coverage gains have been most pronounced in those states, with the share of uninsured adults declining from 18.4% in 2013 to 9.3% in the first nine months of 2016.
By contrast, the uninsured rate for adults declined much more slowly in states that did not expand Medicaid, falling from 22.7% to 17.5%.
Many Republican governors and state legislators have opposed Medicaid expansion, arguing the program is not effective and too expensive, even though the federal government is footing more than 90% of the tab for the expansion.
Congressional Republicans and new Health and Human Services Secretary Tom Price, a former Georgia congressman, have called for dramatic cuts in federal aid for Medicaid.
The new report shows the coverage expansion has also been fueled by new insurance marketplaces, such as HealthCare.gov, that allow Americans who do not get health insurance through an employer to shop for health plans.
Low- and moderate-income consumers qualify for government subsidies to offset the cost of their monthly premiums.
Republicans are also looking to scrap these marketplaces, saying that they are collapsing.
In fact, despite rising premiums in some parts of the country and the departure of some insurers who were losing money, enrollment in the marketplaces has held relatively stable, according to enrollment data.
And many insurance industry officials say the marketplaces could be stabilized.
3:25 p.m.: This article was updated with California figures.