Donald Trump has warned Republicans they could lose their seats in mid-term elections next year if they fail to back his healthcare overhaul and fulfil a long-promised goal to undo Barack Obama's Affordable Care Act.
In a rare trip to the Capitol, the president met behind closed doors with rank-and-file Republicans, some wavering on the legislation two days before a climactic vote.
Senior Republicans in the House of Representatives unveiled revisions to the bill on Monday night in hopes of nailing down support.
One legislator, Walter Jones, said Mr Trump told Republicans their seats could be at risk if the bill fails and "the danger of your not voting for the bill is people could lose their seats".
Speaker Paul Ryan told reporters Mr Trump was "all-in" on repeal-and-replace, and was attending the meeting "to do what he does best: to close the deal".
At a rally on Monday night in Louisville, Kentucky, Mr Trump underscored what he called "the crucial House vote".
"This is our long-awaited chance to finally get rid of Obamacare," he said of repealing Mr Obama's landmark law, a Republican goal since its 2010 enactment. "We're going to do it."
The meeting came as party leaders released 43 pages of changes to a bill whose prospects remain uncertain. Their proposals were largely aimed at addressing dissent that their measure would leave many older people with higher costs.
Included was an unusual approach: language paving the way for the Senate, if it chooses, to make the bill's tax credit more generous for people age 50-64.
The leaders' proposals would accelerate the repeal of tax increases Mr Obama imposed on higher earners, the medical industry and others to this year instead of 2018. It would be easier for some people to deduct medical expenses from their taxes.
Older and disabled Medicaid beneficiaries would get larger benefits, but it would also curb future growth of the overall Medicaid programme, which helps low earners afford medical coverage, and let states impose work requirements on some recipients.
Additional states could not join the 31 that opted to expand Medicaid to more beneficiaries under Mr Obama's law.
The bill would dismantle Mr Obama's requirements that most people buy policies and that larger companies cover workers. Federal subsidies based largely on peoples' incomes and insurance premiums would end, and a Medicaid expansion to 11 million more low-income people would disappear.
The Republican legislation would provide tax credits to help people pay medical bills based chiefly on age, and open-ended federal payments to help states cover Medicaid costs would be cut.
Insurers could charge older consumers five times the premiums they charge younger people instead of Mr Obama's 3-1 limit, and would boost premiums 30% for those who let coverage lapse.
Republican support teetered last week when a non-partisan congressional analysis projected the measure would strip 24 million people of coverage in a decade. The Congressional Budget Office also said the bill would cause huge out-of-pocket increases for many lower earners and people aged 50 to 64.
Democrats have opposed the repeal effort. They tout Mr Obama's expansion of coverage to 20 million additional people and consumer-friendly coverage requirements it imposed on insurers, including abolishing annual and lifetime coverage limits and forcing them to insure seriously ill people.
House approval would give the legislation much-needed momentum as it moves to the Senate, which Republicans control 52-48 but where five Republicans have expressed opposition.