WASHINGTON >> President Donald Trump and his top health official praised the new House Republican health care legislation today, even as surging conservative opposition complicated party leaders’ drive to sell the proposal to rank-and-file lawmakers and the public.

Trump’s morning tweet lauding “our wonderful new Healthcare Bill” kicked off the day. Shortly afterward, Health Secretary Tom Price wrote to the chairmen of the two House committees that wrote the measures, saying “they align with the president’s goal of rescuing Americans from the failures of the Affordable Care Act,” former President Barack Obama’s prized 2010 law.

Yet by lunchtime, conservative lawmakers and others were blasting the bill, underscoring the challenge Republicans face in pushing one of their top priorities to passage.

The legislation would primarily affect some 20 million people who purchase their own private health plans directly from an insurer and the more than 70 million covered by Medicaid, the federal-state program for low-income people.

In the first official though partial measurement to emerge of the bill’s financial impact, Congress’ nonpartisan Joint Committee on Taxation estimated it would cut more than 20 taxes imposed by Obama’s law at a cost of nearly $600 billion over a decade. The bulk of the savings would go to the wealthy.

The estimate did not include the cost of tax credits the measure proposes to help people buy coverage.

Republicans say they’ve not yet received an estimate of the bill’s overall cost or the number of people it would cover from the Congressional Budget Office.

“What Obamacare did was make insurance affordable but care impossible to actually afford,” White House budget chief Mick Mulvaney said on NBC’s “Today Show.” ”The deductibles were simply too high. So people could say they have coverage but they couldn’t actually get the medical care they needed when they get sick.”

“Obamacare” plans did typically come with high deductibles, but the law also provided cost-sharing subsidies to people with modest incomes. Those subsidies will be eliminated under the Republican plan, and it’s unclear how high the deductibles would be under the new approach.

House committees planned to begin voting on the legislation Wednesday, launching what could be the year’s defining battle in Congress and capping seven years of GOP vows to repeal the 2010 Affordable Care Act. Before prevailing, leaders will have to heal internal divisions.

In his letter, Price commended GOP plans to provide millions of Americans with a refundable tax credit — meaning even people without tax liability would receive the assistance. Congressional conservatives have opposed a refundable credit, saying it would create a new entitlement program the government cannot afford.

“It is a missed opportunity and a step in the wrong direction,” said Sen. Mike Lee, R-Utah, one of three conservative senators who’ve criticized GOP leaders for not aggressively repealing Obama’s law. He said it was unknown if the bill would make health care more affordable.

Conservative groups like Heritage Action for America and the Club for Growth also piled on. Club for Growth President David McIntosh called the measure a “warmed-over substitute for government-run health care.”

“As Republicans we have a choice,” House Ways and Means Chairman Kevin Brady, R-Texas, an author of the measure, told reporters. “We can act now or we can keep fiddling around and squander this opportunity to repeal ‘Obamacare.’”

The Republican legislation would limit future federal funding for Medicaid, which covers low-income people, about 1 in 5 Americans. And it would loosen rules that Obama’s law imposed for health plans directly purchased by individuals, while also scaling back insurance subsidies.

Republicans say their solutions would make Medicaid more cost-efficient without punishing the poor and disabled, while spurring private insurers to offer attractive products for the estimated 20 million consumers in the market for individual policies.

Democrats say the bill would make many people uninsured, shifting costs to states and hospital systems that act as providers of last resort. Individual policy holders might be able to find low-premium plans, only to be exposed to higher deductibles and copayments.

The plan would repeal the unpopular fines on people who don’t carry health insurance. It would replace income-based subsidies the law provides to help millions of Americans pay premiums with age-based tax credits that may be skimpier for people with low incomes. Those payments would phase out for higher-earning people.

Thirty-one states and the District of Columbia opted to expand Medicaid coverage under the Obama-era law to an estimated 11 million people. Around half those states have GOP governors, who are largely reluctant to see that spending curtailed.

In another feature that could alienate moderate Republicans, the measure would block for one year federal payments to Planned Parenthood, the women’s health organization long opposed by many in the party because it provides abortions.

In a last-minute change to satisfy conservative lawmakers, business and unions, Republicans dropped a plan pushed by Ryan to impose a first-ever tax on the most generous employer-provided health plans. Instead, a similar tax imposed by Obama’s law on expensive plans set to take effect in 2020 would now begin in 2025.

Popular consumer protections in the Obama law would be retained, such as insurance safeguards for people with pre-existing medical problems, and parents’ ability to keep young adult children on their insurance until age 26.

To prod healthier people to buy policies, insurers would boost premiums by 30 percent for consumers who let insurance lapse.

Associated Press writers Mary Clare Jalonick, Andrew Taylor and Stephen Ohlemacher contributed to this report.