Democrats, claiming a mandate from voters, opened a legislative campaign on Wednesday to secure protections under the Affordable Care Act for people with pre-existing medical conditions, putting aside divisions over a more ambitious push for “Medicare for all” in favor of shoring up existing law.
“Health care was the single most important issue to voters in the 2018 election,” said Representative Anna G. Eshoo, Democrat of California, as she convened a hearing on a decision by a federal district judge in Texas that would invalidate the entire law.
In the court case, filed by Texas and 19 other states, the Trump administration has refused to defend provisions of the Affordable Care Act that protect people with pre-existing conditions.
On the day of the court decision in December, President Trump hailed it as “Great news for America!”
But in his State of the Union address on Tuesday, he said it was now important “to protect patients with pre-existing conditions.” More than any other issue, health care was the policy that united Democratic campaigns last fall, specifically a promise to protect existing law that prohibits insurance companies from charging higher premiums or blocking coverage for customers with pre-existing medical conditions.
Now in charge of the House, Democrats are divided over how far and how fast to go to expand health insurance coverage — and whether to push for a single, government-run system like Medicare for all. But some lawmakers have expressed impatience with the pace of legislative efforts on the one issue they agree on: protecting pre-existing condition coverage.
Experts and ordinary citizens told Congress on Wednesday that Mr. Trump’s position in the Texas court case could be devastating to some patients.
“Families like mine — families with medically complex children — are terrified of what this lawsuit may mean for our kids,” said Elena Hung, whose 4-year-old daughter was born with chronic medical conditions that affect her lungs, heart and kidneys.
“Our lives are already filled with uncertainty — about diagnoses, the effects of medications and the outcomes of surgeries,” said Ms. Hung, who helped found a child advocacy group called Little Lobbyists. “The one certainty we have is the Affordable Care Act and the protections it provides.”
The priorities of the new House majority were on display on Wednesday as three subcommittees held hearings to investigate Mr. Trump’s efforts to dismantle the Affordable Care Act in the last two years.
Democrats said they would try to strengthen the law and restore funds cut by the Trump administration for insurance counselors who help people enroll in health plans. They said they would also try to prevent the White House from granting waivers to state insurance programs that skirt the Affordable Care Act.
Representative Lauren Underwood, a freshman Democrat from Illinois, introduced a bill to increase protections for people with pre-existing conditions. Ms. Eshoo, the chairwoman of the Energy and Commerce subcommittee on health, said she would hold a hearing on it next week.
The bill would overturn a Trump administration rule that has allowed the proliferation of short-term health insurance policies. The policies are allowed to deny coverage or charge higher premiums to people with pre-existing conditions. And they often omit coverage of prescription drugs, mental health care and other benefits guaranteed as essential by the Affordable Care Act.
“A pre-existing condition shouldn’t be some kind of scarlet letter Americans have to wear around their neck as they try to get the quality, affordable health care everyone deserves,” Ms. Underwood said.
Ms. Underwood, a nurse, has a pre-existing condition that occasionally prevents her heart from maintaining a normal rhythm. “So this is personal,” she said. “No insurer should ever have the option to discriminate against us.”
For their part, Republicans said they, too, supported protections for people with pre-existing conditions and wanted to work with Democrats on the issue. But Republican proposals in the past have sometimes offered less protection than the Affordable Care Act provides. They would, for example, have prevented insurers from raising premiums for people with pre-existing conditions — but only if consumers maintained “continuous coverage” without a significant interruption.
A lapse in coverage could have allowed insurers to significantly raise premiums for the sick.
Republicans searched for divisions between Democrats hoping to shore up the Affordable Care Act and more progressive members pushing for a single, government-run insurance system. They taunted Democrats by demanding a public hearing on Democratic proposals for a single-payer health care system, known increasingly as Medicare for all.
“The American people should hear how House Democrats expect to address the massive costs associated with Medicare for all,” said Representative Greg Walden of Oregon, the senior Republican on the Energy and Commerce Committee. “They need to know about the $32 trillion price tag for such a plan and the tax increases necessary to pay for it.”
Some Medicare-for-all proposals could end employer-sponsored health plans that now cover more than 150 million people, Mr. Walden said.
One-third of Senate Democrats and more than half of House Democrats have endorsed proposals to open Medicare to all Americans, as have some of the party’s presidential candidates.
Representative Frank Pallone Jr., Democrat of New Jersey and the chairman of the Energy and Commerce Committee, said it was hypocritical for Republicans to seek hearings on Medicare for all, a plan they oppose as a government takeover of health care.
“Who are you kidding?” Mr. Pallone asked the Republicans. “You’re saying that you want to repeal the Affordable Care Act and then you want to have a hearing on Medicare for all. The cynicism of it!”
At a separate hearing, Representative Robert C. Scott of Virginia, the chairman of the Education and Labor Committee, said the ruling in the Texas case posed a serious threat to people with employer-sponsored coverage.
“All Americans, whether insured through an A.C.A. marketplace or through their employer, would lose the consumer protections we all take for granted,” Mr. Scott said.
Under the Affordable Care Act, employers generally cannot impose a waiting period for coverage of pre-existing conditions. The law requires employers to cover health screenings and other preventive services at no cost to employees, and it prohibits annual and lifetime limits on benefits.
Representative Donna E. Shalala, Democrat of Florida and a former secretary of health and human services, said that Republicans, “despite their long assault on the Affordable Care Act, have yet to develop an alternative that would continue to safeguard more than 133 million Americans with pre-existing conditions.”
California and other states that support the Affordable Care Act have appealed the decision in the Texas case by Judge Reed O’Connor of Federal District Court in Fort Worth.