US Senate Republicans have released a revamped health bill in a bid to rally their divided party around its seven-year campaign to repeal Obamacare.
The plan retains key Obamacare taxes on the wealthy, while allowing insurers to offer less coverage and imposing sharp cuts to healthcare for the poor.
The new bill aims to woo Republicans of conservative and moderate factions.
Congress is delaying its summer holiday in a bid to overturn former President Barack Obamas 2010 legislation.
The latest version of the Republican bill would retain two taxes on people earning more than $200,000 (£155,000), which have helped pay for Obamacare.
Plans for hundreds of billions of dollars in cuts to Medicaid, a healthcare programme for the poor and disabled, are largely unchanged in the Senates revised plan.
The Better Care Reconciliation Act would also provide an extra $45bn to tackle the US opioid epidemic that is wreaking havoc in some Republican senators constituencies.
It includes an additional $70bn to help cover so-called out-of-pocket expenses, which are medical fees not reimbursed by insurers.
Is Obamacare more popular than ever?
The bill also incorporates conservative Senator Ted Cruzs proposal to let insurers offer stripped-down, low-cost healthcare plans by ducking Obamacare rules requiring coverage for "essential" health benefits.
These include maternity and postnatal care, mental health services, addiction treatment, outpatient care, hospitalisation, emergency room visits and prescription drugs.
Insurance companies have warned that Senator Cruzs plan would harm people with pre-existing medical conditions by making their insurance unaffordable.
The Congressional Budget Office found that the previous version of the bill would leave 22 million fewer people insured over a decade.
Senate Republicans are now awaiting a new assessment from the nonpartisan score-keeper.
Can Republicans pass this bill?
The Obamacare repeal has been testing Senate Majority Leader Mitch McConnells reputation as a master tactician.
He must conjure a compromise option that will appease both moderates and conservatives among his rank-and-file.
Democrats are united against the bill, which means that just three "no" votes among Republican senators would sink the legislation.
Republicans have a 52-48 majority in the 100-seat Senate, with Vice-President Mike Pence able to cast any tie-breaking vote.
Senators Susan Collins of Maine and Rand Paul of Kentucky appear firmly opposed to the measure.
Moderate senators such as Rob Portman of Ohio, Shelley Moore Capito of West Virginia and Lisa Murkowski of Alaska are alarmed by the planned Medicaid cuts.
Ten Republicans said they would not support the previous version of the bill.
Underlining the divisions, minutes before Mr McConnell unveiled his plan, two other Republican senators, Lindsey Graham and Bill Cassidy, offered their own healthcare proposal.
Their plan would steer much of the federal funding for health insurance to the states.
President Donald Trump, who made repeal of Obamacare a core campaign pledge, is monitoring the Senate developments while on a visit to France.
He said in an interview on Wednesday he would be "very angry" if he did not get a bill on his desk, exhorting Mr McConnell to "pull it off".
A vote is planned on the bill, should agreement emerge, next week.