U.S. President Donald Trump and Congress face a key moment Monday in the political fight over Republican efforts to repeal and replace the national health care reforms championed by former President Barack Obama.
The Congressional Budget Office, a group of nonpartisan budget analysts and economists, is expected to release its assessment of how many Americans would lose their health insurance coverage if Trump and his Republican colleagues in Congress are successful in upending the 2010 law under which 20 million previously uninsured people now have policies to help pay their medical bills.
Its independent analysis often plays a key role in the U.S. legislative process, giving lawmakers an idea of how costly prospective laws might prove to be in the coming decade or what other effects the measures would have.
WATCH: Trump on failure of Obamacare
Trump has promised that his health plan will "cover everybody" and offer cheaper insurance policies for individuals and small groups of people who buy insurance for themselves rather than getting coverage through their employers, which is the most common way Americans have health care insurance.
House of Representatives Speaker Paul Ryan has said that fewer people will have insurance under the plan he is pushing with Trump's support.
Outside analysts who have examined the proposal being advanced by House Republicans and the new president say it could increase the ranks of the uninsured by as many as 15 million people. But the Congressional Budget Office assessment is the official "score" that many lawmakers consider to be the most important.
In a comment on his Twitter account, Trump contended that his predecessor's signature legislation, popularly known as Obamacare, "is imploding." He added, "It is a disaster and 2017 will be the worst year yet, by far! Republicans will come together and save the day."
ObamaCare is imploding. It is a disaster and 2017 will be the worst year yet, by far! Republicans will come together and save the day.— Donald J. Trump (@realDonaldTrump) March 13, 2017
The president staged a "listening session" at the White House with people who said they had had bad experiences with high costs under Obamacare. Trump told them his proposal over time would give them "more choices at lower costs. It's going to be a thing of beauty."
With early projections that the Republican proposal could cost millions of people their insurance and actually make insurance policies more costly for some, the White House last week sought to downplay the pending official budget office conclusion.
"If you're looking to the CBO for accuracy, you're looking in the wrong place," Trump spokesman Sean Spicer said. He noted that the agency had overestimated insurance enrollment under Obama's law.
The CBO also will estimate the cost of the Republican plan for the federal government, which could augur well for the Trump repeal efforts if it suggests that changes in the Obama law would save the government money over the next 10 years. But if the opposite is true, then the repeal efforts could prove to be more difficult in Congress.
Republicans especially want to overturn the Obamacare provision that all Americans buy insurance or pay a penalty if they do not, a requirement that conservative lawmakers view as an intrusion by the national government on the individual liberties of Americans.
They also want to offer low-income Americans tax credits to buy insurance but over the next few years curtail government spending on health care for poorer Americans, leaving individuals to pay more out of their own pockets for their medical bills than under the current law.
However, the Republican lawmakers want to retain two of the most popular features of Obamacare: banning insurers from refusing to write policies for anyone because of a pre-existing medical condition, and allowing young people to stay on their parents' policies until they turn 26.