Republicans in the House of Representatives have advanced US President Donald Trump's massive tax-cut and spending bill towards a final yes-or-no vote, appearing to overcome internal party divisions over its cost.
Following a day of closed-door meetings both on Capitol Hill and at the White House, lawmakers cleared a final procedural hurdle needed to begin debate on the bill in a 219-213 vote early on Thursday morning.
Lawmakers then reopened debate for a final vote that was expected a couple of hours later.
An earlier procedural vote was held open for seven hours on Wednesday, giving Trump and House Speaker Mike Johnson time to convince holdouts to back the president's signature bill.
Trump expressed frustration with the slow passage of the bill and lashed out at congressional Republicans on social media, warning them they would lose MAGA votes if the bill died.
Johnson had expressed optimism on Wednesday night, saying lawmakers had a "long, productive day" discussing the issues.
After the vote he praised Trump for making phone calls to the holdouts through the early hours of Thursday morning.
"There couldn't be a more engaged and involved president," Johnson told reporters.
The Senate passed the legislation, which nonpartisan analysts say will add $US3.4 trillion ($A5.2 trillion) to the nation's $US36.2 trillion in debt over the next decade, by the narrowest possible margin on Tuesday after intense debate on the bill's hefty price tag and $US900 million in cuts to the Medicaid healthcare program for low-income Americans.
With a narrow 220-212 majority, Republicans can afford no more than three defections to get a final bill passed.
Democrats are united in opposition to the bill, saying that its tax breaks disproportionately benefit the wealthy while cutting services that lower- and middle-income Americans rely on.
The non-partisan Congressional Budget Office estimated that almost 12 million people could lose health insurance as a result of the bill.
"This bill is catastrophic. It is not policy, it is punishment," Democratic Representative Jim McGovern said in debate on the House floor.
Republicans in Congress have struggled to stay united in recent years, but they also have not defied Trump since he returned to the White House in January.
Any changes made by the House would require another Senate vote, which would make it all but impossible to meet the July 4 deadline.
The legislation contains most of Trump's top domestic priorities, from tax cuts to immigration enforcement.
The bill would extend Trump's 2017 tax cuts, cut health and food safety net programs, fund Trump's immigration crackdown, and zero out many green-energy incentives. It also includes a $5 trillion increase in the nation's debt ceiling, which lawmakers must address in the coming months or risk a devastating default.
The Medicaid cuts have also raised concerns among some Republicans, prompting the Senate to set aside more money for rural hospitals.