Vice President Mike Pence joins the Senate GOP leadership, Sen. John Thune, R-S.D., left, and Senate Majority Leader Mitch McConnell of Ky., as Republicans introduce their plan to repeal and replace the Affordable Care Act, President Barack Obama's signature health care law, Tuesday, March 7, 2017, on Capitol Hill in Washington. (AP Photo/J. Scott Applewhite)

WASHINGTON — 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 will convene what are expected to be marathon sessions today 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 was launched, 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. “Passing it would be making the same mistake that President Obama, Harry Reid and Nancy Pelosi made in 2010.

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 Capitol Hill.

Closer to the political center, Ohio’s Republican Gov. John Kasich expressed deep doubts in a statement that took issue with congressional plans to curb Medicaid coverage expanded under Obama.

“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,” said Kasich.

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

AARP also objected, saying the bill would “dramatically increase health care costs for Americans aged 50-64” 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.

Meanwhile, the U.S. Chamber of Commerce sent congressional leaders a letter praising the GOP 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, with Senate Minority Leader Chuck Schumer of New York saying 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 Americans covered under Obamacare.

“We’re going to do something that’s great and I’m proud to support the replacement plan released by the House of Representatives,” Trump declared at the White House as he met with the House GOP vote-counting team Tuesday. “We’re going to take action. There’s going to be no slowing down. There’s going to be no waiting and no more excuses by anybody.”