The US House of Representatives will hold a vote on Thursday on a revised healthcare bill that Republicans hope will replace Obamacare.
House Majority Leader Kevin McCarthy said the party’s leadership believed it had enough votes for the bill to pass, despite opposition from Democrats.
It would then go to the Senate where it could run into more difficulties.
President Donald Trump made the repeal of his predecessor’s signature law a central campaign promise.
He has played a personal role this week in persuading wavering Republicans to come on board the legislation, known as the American Health Care Act (AHCA).
What is in the revised bill?
In an effort to win votes of Republicans who were against the initial healthcare bill, Republicans amended it several times, trying to balance the different demands.
Several key Republicans then reversed course, partly due to an amendment by Congressman Fred Upton.
It provides $8bn (£6.2bn) over five years towards coverage for sick people, including those with cancer, who could otherwise face higher costs under the new system.
But health policy experts say the amount is not enough to cover the cost of coverage for the sickest patients.
The American Medical Association said millions of people would lose their coverage as a result of the proposal.
“None of the legislative tweaks under consideration changes the serious harm to patients and the health care delivery system” that the bill could cause, the association’s president Andrew W. Gurman said in a statement.
Where do Democrats stand?
No Democrats support the revision, and say the amount provided by the Upton amendment is inadequate.
Senate minority leader Chuck Schumer said: “The Upton amendment is like administering cough medicine to someone with stage four cancer.”
That means the 216 votes necessary to pass the legislation will have to come from Republicans, who control both legislative chambers in Congress.
But internal differences remain, and they can afford only 22 defections. Reports suggest that 18 Republicans are likely to vote against the bill, and at least 33 are undecided or have no clear position.
The vote will happen without an estimate from the nonpartisan Congressional Budget Office of how many people will be left uninsured under the new plan and how much it will cost.
In March, it said 24 million people would lose health insurance under the initial bill.
Why did the first bill fail?
The first attempt collapsed in disarray in March, with opposition from both moderates and conservatives inside the Republican party.
They feared too many people with pre-existing medical conditions would be left unable to afford health coverage.
President Barack Obama’s overhaul of healthcare extended insurance coverage to millions of Americans, but some have experienced rising premiums in recent years.
One of its popular elements is that it bans insurers from denying coverage to patients who are ill with “pre-existing conditions”.
President Trump has insisted the revised bill will keep that, although it is thought that states will be able to opt out of making that an absolute provision.
Conservatives want to see a complete rollback of Obamacare, while moderates are concerned about losing voters who like the existing law.
Comedian Jimmy Kimmel made a heartfelt plea that pre-existing conditions be protected, and spoke about his newborn son who has a congenital heart defect, in a video that has been widely shared on social media.
Trump in the White House
Crucial House vote to be held on Obamacare repeal bill