WASHINGTON >> President Donald Trump declared Monday that “Nobody knew that health care could be so complicated.” Yet the opposite has long been painfully obvious for top congressional Republicans, who face mounting pressure to scrap the law even as problems grow longer and knottier.

With the GOP-controlled Congress starting its third month of work on one of its marquee priorities, unresolved difficulties include how their substitute would handle Medicaid, whether millions of voters might lose coverage, if their proposed tax credits would be adequate and how to pay for the costly exercise.

The nonpartisan Congressional Budget Office made their job even dicier recently, giving House Republicans an informal analysis that their emerging plan would be more expensive than they hoped and cover fewer people than former President Barack Obama’s statute. The analysis was described by lobbyists speaking on condition of anonymity to discuss private conversations with congressional aides.

For many in the party, those problems — while major — are outweighed by pledges they’ve made for years to repeal Obama’s 2010 law and substitute it with a GOP alternative. Conservatives favoring full repeal are pitted against more cautious moderates and governors looking to curb Medicaid’s costs also worry about constituents losing coverage. But Republicans also see inaction as the worst alternative and leaders may plunge ahead as soon as next week with initial House committee votes on legislation.

“I believe they have left themselves no choice. Politically they must do something,” Douglas Holtz-Eakin, a Republican economist and health analyst, said Monday.

Trump spoke about health care’s complexities on a day he held White House talks with dozens of governors worried Republicans could shift a huge financial burden to the states by curbing Medicaid, the federal-state program that helps low-income people and those in nursing homes pay bills. Republican governors told reporters later that Trump would describe some specifics of his own health care plan in an address Tuesday to a joint session of Congress.

Trump also met with insurance company executives concerned that uncertainty about possible GOP changes could roil the marketplace. Insurers said they remain committed to working with the administration and the GOP-led Congress.

Trump said the current health insurance market is “going to absolutely implode”— a contention he and other Republicans have made repeatedly. With premiums, deductibles and other out-of-pockets costs increasing in many individual markets, Democrats concede that changes are needed. But they contest that dire description and have shown no interest in helping Republicans kill Obama’s statute.

Senate Minority Leader Chuck Schumer, D-N.Y., told reporters Monday that Republicans have yet to win any Democratic support for their effort and said “the odds are very high” Obama’s law won’t be repealed.

Congress returned Monday from a recess that signaled that the GOP faces a lot of difficulties in its task.

Many Republicans received rough receptions at town hall meetings from activist backers of Obama’s overhaul. Governors meeting in Washington received a consultants’ report warning that planned Republican cuts in Medicaid and federal subsidies for consumers buying private insurance would risk coverage for many people and serious funding gaps for states.

Sen. Lisa Murkowski, R-Alaska, said she wouldn’t support blocking federal payments to Planned Parenthood or repealing the health law’s expansion of Medicaid — two staple GOP proposals. And former House Speaker John Boehner, R-Ohio, predicted at a Florida health care forum last week that full repeal and replacement of Obama’s law is “not going to happen” and suggested they’d end up leaving much of the law intact.

The plan House Republicans are considering includes helping people pay doctors’ bills with tax credits based on age, not income, and expanding tax-advantaged health savings accounts. They would also end Obama’s expansion of Medicaid to more low earners and the open-ended federal payments states currently receive to help pay for the program.

Although “Obamacare” has never been popular, public opinion polls show most Americans want changes but not a complete takedown of the law. Consumers are unhappy that Obama’s statute did not tame the problem of costs but don’t see taking coverage away as the answer.

At the same time, a number of Republican governors have taken a different path from the congressional GOP. Instead of insisting that the law be repealed, they reached accommodations with the previous administration that allowed the statute’s Medicaid expansion to proceed in their states. According to the nonpartisan Kaiser Family Foundation, there are now 16 states with GOP governors that have expanded Medicaid.

The consequences of GOP actions could make many people unhappy — not just the 20 million covered through the law but insurers, hospitals and drug companies who have benefited from Obamacare.

“Republican governors who took the expansion could be held responsible if hundreds of thousands of people lose coverage,” said Robert Blendon of the Harvard T.H. Chan School of Public Health, an expert on public opinion about health care.