While the law mostly remains intact, Democrats have said the administration's reluctance to fund outreach and educational programs has depressed enrollment via federal exchanges.
"President Trump's cruel health care sabotage has left 2 million more people without health insurance, forced to live in constant fear of an accident or injury that could spell financial ruin for their families," said House Speaker Nancy Pelosi, D-Calif.
Added Senate Democratic Leader Chuck Schumer, D-New York: "The relentless effort by Republicans to sabotage our health care system has resulted in millions of fewer Americans with health insurance and skyrocketing costs for American families."
According to the Census Bureau, about 25.6 million didn't have coverage at any point during 2017, the Trump administration's first year. That number increased to 27.5 million -- almost 8.5% of Americans -- last year.
It's the first year-to-year increase since 2008 to 2009, according to the report.
Ed Haislmaier, a senior research fellow at the right-leaning Heritage Foundation, called the survey data "questionable" and said it conflicts with other administrative data released by the federal government. He said there's evidence that about 1.6 million people have dropped Medicaid, the government's health care program intended for low-income and disabled Americans, as well as the Children's Health Insurance Program, or CHIP, in one year.
That potential drop in Medicaid and CHIP enrollments is likely due to an improved economy and that some of those people no longer qualify, he said. Worth noting, too, is that those 1.6 million Americans no longer enrolled in Medicaid or CHIP aren't necessarily going without insurance or health care, he said.
"Uninsured does not mean people don't get care," Haislmaier said.
In an interview with ABC News last June, Trump called the current health care law a "disaster" and said he would revamp it if the GOP regained a majority in the House. It remains unclear, however, for which specific plan the president would advocate. A GOP-led health care bill failed under his presidency when Republicans held control of both chambers.
"If we win back the House, we're going to produce phenomenal health care," he told ABC News' George Stephanopoulos. "And we already have the concept of the plan, but it'll be less expensive than Obamacare by a lot."
Last June, Trump signed an executive order aimed at curbing health care costs by requiring health insurers and providers to reveal pricing for care to patients. He said it would "blow everything away" in the health care industry.
Looking ahead to the 2020 campaign, Democrats have seized on health care -- particularly the rising cost of prescription drugs -- as an issue where they think they can sway voters.
According to Kaiser Health News, enrollment in states that use the federal healthcare.gov platform has been sluggish in 2018 compared to 2017. From Nov. 1 through Dec. 1, about 3.2 million people had chosen plans for 2019. Compared with the previous year, that's about 400,000 fewer, a drop of just over 11%. The wider availability of short-term plans was one big change, as well as the elimination of the penalty for not having health insurance.
Haislmaier said the data doesn't support Democratic claims that Trump's policies or funding of outreach programs are culpable in suppressing enrollment in federal health care exchanges under the Obama-era law.
"When you look at all the trends," he added, "it's pretty much flatlined for three years."