WASHINGTON (AP) — Over the strong objections of key conservatives and Democrats, House Republican leaders are forging ahead with a health care plan that scraps major parts of the Obama-era overhaul.

The House Ways and Means Committee and the Energy and Commerce Committee intended to convene what were expected to be marathon sessions Wednesday to start voting on the legislation.

President Donald Trump and Vice President Mike Pence back the plan to repeal Barack Obama's health care law, and Speaker Paul Ryan, R-Wis., is confidently predicting it will pass the House.

But many fellow Republicans don't seem to be listening.

On Tuesday, less than 24 hours after the GOP health bill came out, a powerful conservative backlash threatened to sink it.

"As the bill stands today, it is Obamacare 2.0," according to a statement by the billionaire Koch Brothers'-backed Americans for Prosperity and FreedomWorks groups. "Millions of Americans would never see the improvements in care they were promised, just as Obamacare failed to deliver on its promises."

Those sentiments were echoed by some GOP lawmakers on the right.

Closer to the political center, Gov. John Kasich. R-Ohio, expressed deep doubts in a statement that took issue with plans to curb Medicaid coverage expanded under the former president.

"Phasing out Medicaid coverage without a viable alternative is counterproductive and unnecessarily puts at risk our ability to treat the drug-addicted, mentally ill and working poor who now have access to a stable source of care," Kasich said.

"The right way to fix Obamacare is by Republicans and Democrats working together," he added.

At the White House meeting Tuesday, Trump made clear to House Republicans that he would be personally engaging with individual lawmakers who oppose the bill as the party's leadership tries to round up votes, according to a lawmaker present who spoke on condition of anonymity to discuss the private gathering.

Not long after, Trump appeared to be making good on his promise, tweeting at Sen. Rand Paul, R-Ky., who has criticized the bill.

"I feel sure that my friend @RandPaul will come along with the new and great health care program because he knows Obamacare is a disaster!" Trump wrote.

He plans to reconvene the group next week and was to meet with conservative leaders Wednesday to discuss the issue.

Opposition was building among influential groups.

The American Medical Association said Wednesday that the bill "would result in millions of Americans losing coverage and benefits," while making coverage "more expensive — if not out of reach — for poor and sick Americans."

AARP said the bill would "dramatically increase" health care costs for people age 50 to 64, and put the health care of millions at risk. The organization, which has nearly 38 million members, was pivotal to the passage of Obama's law in 2010.

But the U.S. Chamber of Commerce sent congressional leaders a letter in praise of the plan, calling it "absolutely critical in taking steps to restore choice, flexibility and innovation to the nation's health care markets."

Democrats remained unified in opposition. Senate Minority Leader Chuck Schumer of New York said the Republican approach would mean "higher cost for less health care, plain and simple."

Republicans are pushing forward even without official estimates from the Congressional Budget Office on the cost of the bill and how many people would be covered, although GOP lawmakers acknowledge they can't hope to match the 20 million people covered under the health law.

Aiming to reduce the role of government in health care, the GOP plan would repeal unpopular fines that Obama's law imposes on people who don't carry health insurance. It would replace income-based subsidies, which the law provides to help millions of people 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.

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

Democrats say the bill would leave many people uninsured, shifting costs to states and hospital systems that act as providers of last resort. The bill also adds up to big tax cuts for the rich, cutting more than 20 taxes enacted under Obama's heath law with the bulk of the savings going to the wealthiest Americans.

Conservatives say the GOP's new system of refundable tax credits would be a costly new entitlement, and they're demanding a vote on a straightforward repeal-only bill.

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