That number is expected to jump to 24 million more by 2026, compared with the current law, the Affordable Care Act, President Obama's signature legislation, for a total of 52 million uninsured that year, according to the CBO.
One of the biggest differences between the proposed health care plan and the Affordable Care Act is that there would be no penalty for people who do not have health insurance. The CBO says lifting that requirement would be one of the biggest factors contributing to the increase in the number of uninsured.
"Most of that increase would stem from repealing the penalties associated with the individual mandate. Some of those people would choose not to have insurance because they chose to be covered by insurance under current law only to avoid paying the penalties, and some people would forgo insurance in response to higher premiums," the report states.
The GOP plan would decrease the federal deficit by $337 billion from 2017 to 2026, according to the CBO.
House Speaker Paul Ryan, who has been one of the biggest champions of the proposed AHCA, said the report confirms that the GOP plan "will lower premiums and improve access to quality, affordable care."
"I recognize and appreciate concerns about making sure people have access to coverage. Under Obamacare, we have seen how government-mandated coverage does not equal access to care, and now the law is collapsing. Our plan is not about forcing people to buy expensive, one-size-fits-all coverage. It is about giving people more choices and better access to a plan they want and can afford," he said in a statement shortly after the CBO report was released.
The CBO is a nonpartisan agency that produces economic projections and federal spending and revenue estimates for pending legislation.
Trump administration officials were quick to decry portions of the analysis, with Secretary of Health and Human Services Tom Price saying they "disagree strenuously with the report."
"We believe that our plan will cover more individuals at a lower cost and give them the choices that they want for the coverage that they want for themselves and their families, not that the government forces them to buy," he said.
But as Price and Office of Management and Budget Director Mick Mulvaney contested portions of the report that indicated the number of uninsured Americans would rise, they lauded the findings showing that premiums would eventually fall.
"One of the things we have said about this proposal from the beginning was that we believed — for some reasons that have been basic tenets of Republican conservative thought for a long time — that competition lowers cost," said Mulvaney. "What the CBO just told us is that's exactly right."
Price and Mulvaney stressed that the report doesn't take into account all the phases of the repeal and replace efforts but said that lawmakers should not disregard the findings.
Asked at today's White House press briefing if the numbers are legitimate, Spicer said, "All I'm suggesting to you is the numbers they did the last time they did health care were off by more than 50 percent when it came to the number of people insured. That's not my interpretation. That's a fact."
That report from the CBO on Obamacare, in March 2010, was far off in its estimates of marketplace enrollment. That year the office projected that by 2016, 21 million people would have health insurance via the Affordable Care Act marketplaces, but the actual number was closer to 12 million.