The estimates on the impact on the federal budget deficit reflects the savings that would accrue from a reduction in federal spending on Obamacare subsidies to millions of customers, which would be offset on the revenue side somewhat by elimination of ACA-related taxes.
The CBO's projections come days after the Brookings Institution estimated that the the bill would increase the number of uninsured Americans by more than 15 million, and the Joint Committee on Taxation estimated it would cost the federal government an additional $600 billion over a decade.
In anticipation of the estimates about the loss of insurance by millions, backers of the bill sought to delegitimize the CBO's analysis.
That critique of the CBO conflicts with the fact that members of Congress of both parties for the past four decades have depended on the office to provide analyses of budgetary and economic issues.
"If you're looking to the CBO for accuracy, you're looking in the wrong place," White House press secretary Sean Spicer said last week.
Mick Mulvaney, director of the White House Office of Management and Budget, said, "If the CBO was right about Obamacare to begin with, there'd be 8 million more people on Obamacare today than there actually are."
"Sometimes we ask them to do stuff they're not capable of doing, and estimating the impact of a bill of this size probably isn't the best use of their time," Mulvaney said.
The CBO's analysis comes a week after the bill was introduced by Republican leaders in the House of Representatives, and passed by two committees. The bill is headed to review by the House Budget Committee this week.
The American Health Care Act is being supported by Ryan and other key members of the House, in addition to Trump.
Trump, Ryan the other leaders in the past week have repeatedly described Obamacare as a failing program that has led to skyrocketing insurance premiums, and millions of people being unable to use their coverage because of unaffordable deductibles.
Before the CBO released its score for the replacement plan, Trump tweeted new criticism of Obamacare.
Andy Slavitt, who oversaw Obamacare as head of the federal Centers for Medicare and Medicaid Services in the Obama administration, said the CBO report "seems like one of the first major domestic leadership tests for President Trump."
"Does he give in to traditional D.C. political pressures and push a bill that there is now strong evidence would harm millions of Americans in small towns and big cities around the country, or does he show the leadership to step back and figure out what's best for the American public?" Slavitt asked.
While many Republicans agreed with Trump's broad critique of the Affordable Care Act, the Republican bill has been greeted by criticism from many GOP conservatives, in addition to liberal supporters of Obamacare.
The conservative case against the bill is that it does not go far enough in repeal in the ACA because it would continue to issue subsidies, albeit in reduced amounts, to people to help them buy individual health insurance plans. Conservatives also do not want to delay the rollback of Medicaid funding until 2020.
But in the Senate, several GOP senators have said they will not support a replacement bill that does not protect coverage gains made by Medicaid under Obamacare. Other Republican senators object to defunding of Planned Parenthood, as the GOP bill would do.
Tom Price, the secretary of the Department of Health and Human Services, said on NBC's "Meet the Press" on Sunday that, "There are a lot of people that are worse off right now when they're paying for health care and they aren't getting the care that they need," Price said.
"Again, the premiums are up and deductibles are up. If you're an individual out there making fifty, sixty thousand dollars and your deductible is eight, ten, twelve thousand bucks you may have that insurance card, but you don't have coverage," Price said.
"And I hear from my former colleagues all the time about patients who come into their office and they recommend something for them, and they're not able to get it because the deductible is so high."
Price also said he did not expect that the Republican plan would result in higher costs of insurance, and that he does expect an increase in the number of people with health insurance.
"I firmly believe that nobody will be worse off financially," Price said. "There's coverage that's going to go up."
When asked about the Brookings Institution estimate that more than 15 million people would become uninsured as a result of the GOP plan, Price said, "I'll tell you that the plan that we've laid out here will not leave that number of individuals uncovered."
"In fact I believe, again, that we'll have more individuals covered," Price said.
Obamacare led to unprecedented drops in the nation's uninsured rates through a combination of measures.
The first measure to take effect was the provision that allows people under the age of 26 to be covered by their parents' health plans.
The ACA's so-called individual mandate requires most people to have health coverage of some kind — such as through a job, an individual insurance plans, Medicare, Medicaid, or military insurance — or pay a tax penalty. For the 2016 tax year, that penalty is the higher of $695 or 2.5 percent of household income.
Obamacare also authorized the creation of government-run insurance marketplaces, which sell individual plans offered by private insurance companies. Customers of those marketplaces, also known as exchanges, can get federal subsidies that lower the cost of their monthly premiums if they have low and moderate incomes. Lower-income customers can get additional subsidies for their out-of-pocket health expenses.
Medicaid expansion has been credited with having the largest impact on reducing the number of uninsured people.
More than 10 million Americans are estimated to have gained coverage through the ACA provision that allows states to loosen eligibility requirements for their Medicaid programs so that nearly all poor adults can sign up for them. Thirty-one states, along with the District of Columbia, have expanded their Medicaid programs.