WASHINGTON — Republican leaders embarked on an ambitious plan Tuesday to try to sell their new health care proposal to rank-and-file lawmakers and the public, absent specifics on costs or how many Americans will be covered.

President Donald Trump’s early morning tweet praising “our wonderful new Healthcare Bill” started off the day, and GOP leaders planned a news conference to promote the plan ahead of Wednesday’s committee action.

The new bill aims to replace “Obamacare” with a system designed along conservative lines. Primarily affected would be 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.

White House budget chief Mick Mulvaney said Tuesday it’s unfair to compare how many people would have health insurance under the new Republican plan to those under the existing health law that Republicans have long derided as “Obamacare.”

“What Obamacare did was make insurance affordable, but care impossible to actually afford,” 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.

Mulvaney said that while the nonpartisan Congressional Budget Office hasn’t yet determined the cost of the new health care bill, it will bring “tremendous long-term savings” by giving states more control over Medicaid, the joint federal-state program for low income Americans.

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 former President Barack 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.

But 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.