A new analysis that at least 18 million people could lose health insurance in the first year if Congress repeals the Affordable Care Act without replacing it intensified the battle this week over the landmark health-care law as President-elect Donald Trump and Republicans try to figure out how to dismantle it.

Democrats seized on the report, issued Tuesday by the nonpartisan Congressional Budget Office, to discredit Republican efforts to repeal Obamacare and rally Americans who are insured under the program. The report underscored the political peril that Trump faces in trying to meet one of his top campaign promises — and also the discord among Republicans about how to do it.

The political and public-relations battle over the ACA is now at full speed, with Democrats holding rallies across the country and inviting Americans to Capitol Hill to describe how their lives were improved or even saved by the law. Republicans, meanwhile, accused Democrats of distorting the truth about the much-debated program — but also revealed signs of disunity about how to meet their promise of repeal without political fallout among voters or economic calamity in the insurance market.

Trump waded into the fray over the weekend when he declared that his own replacement plan is nearly complete — touting the goal of “insurance for everybody” and promising “much lower deductibles” for consumers. That pronouncement appeared to come with little consultation with congressional Republicans, and it conflicted directly with plans laid out by Trump’s advisers, including Rep. Tom Price (R-Ga.), his nominee for secretary of health and human services.

See how your coverage could be impacted by four prominent plans proposed by Republicans

On Wednesday, the battleground moves to the Senate, where members of the Health, Education, Labor and Pensions Committee will question Price about the U.S. health-care system.

While the courtesy hearing will address a variety of issues — including several of Price’s stock trades in health-care firms, which have sparked questions about a possible conflict of interest — it will provide a forum for both parties to delve into what will happen once Republicans repeal key parts of the Affordable Care Act.

The fact that Trump has begun to sketch out his own health-care proposal has injected a new element of uncertainty in an evolving fight that could have serious implications for other parts of Trump’s policy agenda.

Several Republicans sounded cautious about some of the president-elect’s more sweeping promises and said there had been only limited consultation between the transition team and key congressional committees.

Senate Finance Committee Chairman Orrin G. Hatch (R-Utah) told reporters that it is difficult to commit to providing universal health coverage in any upcoming GOP replacement. In 2012, Hatch said it was a “disgrace” that so many Americans were uninsured, “but we cannot succumb to the pressure to argue on the left’s terms.”

“It would be wonderful if we could do that,” Hatch said Tuesday. “We’ve never been able to do that before.”

Sen. Lamar Alexander (R-Tenn.), who leads the committee before which Price will appear Wednesday, said he has not heard any details of Trump’s plan.

“I thought that was a very interesting observation, and I’m going to wait until I actually see his plan in February” before commenting on it, Alexander said.

Some congressional Republicans have been more vocal in recent days about concerns that they are hearing from constituents on what comes after the law is repealed. Several also suggested that Democrats are deliberately spreading misinformation.

“I think you hear from two categories,” said Sen. Charles E. Grassley (R-Iowa). “One are people that think Medicare is going to be affected, and obviously we haven’t made very clear that there’s absolutely no connection with Medicare. And the other one is dealing with the people they think are going to lose their insurance as soon as we . . . repeal.”

Democrats are eager to use the uncertainty about what would take the ACA’s place to their political advantage.

Sen. Debbie Stabenow (D-Mich.) will co-host a forum Thursday with Sens. Elizabeth Warren (D-Mass.) and Patty Murray (D-Wash.) on Capitol Hill featuring “Americans from across the country who would be hurt by healthcare repeal and the policies supported by Congressman Price.”

“They’re coming to the realization that it’s really easy to tear down the house and much more difficult to build it,” Stabenow said of Republicans. “Having ideas doesn’t make a plan. Having five plans doesn’t make a plan.”

Senate Democrats called on Republicans to delay Price’s initial hearing Wednesday, but Republicans said they would proceed with it, and they set a final confirmation hearing for Jan. 24.

They also held up the new CBO report as evidence that millions could lose coverage if Republicans press ahead with their repeal plan. But AshLee Strong, a spokeswoman for House Speaker Paul D. Ryan (R-Wis.), called the report “meaningless” because it amounted to an update of an analysis of a 2015 repeal bill and “takes into account no measures to replace the law nor actions that the incoming administration will take to revitalize the individual market that has been decimated by Obamacare.”

The 2015 bill passed both chambers, but President Obama vetoed it.

Sen. Thom Tillis (R-N.C.) said Democrats are deliberately misleading voters.

“This whole false narrative of all of a sudden having 20 million people get sick because you’re not going to have some sort of solution to them means they are not reading their briefings or they’ve got really subpar people in the marketing department,” he said.

Price and Sen. Bill Cassidy (R-La.) have previously introduced legislation to replace the ACA, and both Ryan and Hatch, who sits on the health committee, have drafted white papers outlining possible paths forward. These plans have several elements in common, including eliminating limits on deductibles and the requirement that individuals buy coverage, establishing private health savings accounts and converting federal premium subsidies to flat tax credits.

But some of these proposals — along with others such as curtailing the expansion of Medicaid coverage and reversing changes the ACA made to Medicare — could alienate voters, and in places they could contradict Trump’s plans for a replacement bill. While repealing the president’s signature health-care law has been a central goal of the conservative movement for the past six years, many of the Americans who helped vote Trump into office benefit from federal health programs and the subsidies that flow from the law.

Ezekiel Emanuel, who served as a top White House health-care adviser during Obama’s tenure and has met with Trump as well as his aides, said in an interview Tuesday that the president-elect is sincere about the idea of “repeal and replace” when it comes to the ACA, rather than just “repeal and delay.”

“He does want to get universal coverage,’” said Emanuel, who leads the University of Pennsylvania’s Department of Medical Ethics and Health Policy. “He wants something he can be proud of.”

Drew Altman, president and chief executive of the Henry J. Kaiser Family Foundation, said it is “technically very difficult to come up with a plan that achieves Republican goals” of lowering the cost of insurance premiums without generous federal subsidies “and also the goals of the ACA,” which expand what kind of services are covered.

As Trump works to deliver on his promises, this week it is Price — a 62-year old congressman from the affluent northern Atlanta suburbs — who will serve as the face of the incoming administration.

The former orthopedic surgeon has staked out controversial positions on Medicare, Medicaid and tax breaks for employer-sponsored health plans. In his most recent health-care bill, Price proposed eliminating the Medicaid expansion under the ACA that has provided new coverage to roughly 10 million Americans and abolishing provisions under the law that provided more comprehensive prescription drug coverage to Medicare recipients.

A transition official, who spoke on the condition of anonymity because Price has yet to be confirmed, said that if Price wins Senate approval to head the Department of Health and Human Services, he “will focus on running the agency, implementing legislation and advancing the president’s priorities.”

Several Senate Republicans have said that any major changes to Medicare will be considered separately from the effort to dismantle and replace the ACA.

“This is not the bill for Medicare reform,” Alexander said on the Senate floor last week.

Democrats have also raised concerns about Price’s investments in health-care firms. In December, the Wall Street Journal reported that Price had traded more than $300,000 in shares in about 40 health, biomedical and pharmaceutical companies over a four-year period starting in 2012, while he was involved with legislation that might affect those firms’ stocks. On Monday, CNN reported that he had bought shares in a medical-device manufacturing company, Zimmer Biomet, a matter of days before introducing legislation that would benefit the firm.

Senate Minority Leader Charles E. Schumer (D-N.Y.) said the trades suggested “a clear and troubling pattern” on Price’s part, and he asked the Office of Congressional Ethics to investigate the Zimmer Biomet trade, which he called possibly “illegal.”

Transition spokesman Phillip Blando noted that the trade “was broker-directed, not directed by Dr. Price,” and said the congressman was not aware of the purchase until after introducing his bill. In a letter on Tuesday, Trump’s aides wrote that “The Presidential Transition Team requests that CNN retract this blatantly false story.”

Hatch dismissed any concerns about Price’s investments.

“It’s total BS,” he said. “Everybody here knows he’s an honest guy. He’s disclosed everything. What more can he do?”

Kelsey Snell contributed to this report.