Senior Democrats say they are confident they have enough votes to pass landmark healthcare reform legislation in the US House of Representatives.
The House is set to vote later on the highly-contested bill, which would give health coverage to 32m more Americans.
Top Democrats, including President Barack Obama, have spent days working to get the 216 votes needed to pass it.
Democratic House Caucus leader John Larson said: “We have the votes. We are going to make history today.”
Democratic Majority Leader Steny Hoyer also told the NBC news network he was confident the party had sufficient votes to pass the measure.
It comes a day after Mr Obama visited Capitol Hill to rally support among party members, saying: “Let’s get this done.”
The Republicans are unanimously opposed to the legislation, which they say is unaffordable and represents a government takeover of a large part of the country’s economy.
Senior House Republican Mike Pence told CNN he was doubtful the Democrats did have the votes needed to approve the bill and said his party would do whatever it could to prevent its passage.
Eric Cantor, the second-ranking Republican in the House, told ABC: “The American people don’t want this to pass. The Republicans don’t want this to pass. There will be no Republican votes for this bill.”
The House will hold three votes – one on a Senate version of a health reform bill, one on a package of changes that would be made to that bill and one on the rules that will govern the debate.
If all three are passed, Mr Obama will be able to sign the legislation into law.
Democratic Senate Majority Leader Harry Reid assured House lawmakers on Saturday he had the “commitment of a significant majority” in the Senate to ensure the package of changes the House wants to its bill will pass there.
The BBC’s Richard Lister in Washington says that whatever happens, this will be a significant day in American politics.
Either healthcare will be significantly reformed, he says, or reform will be kicked into the long grass for perhaps decades to come – which could have all kinds of budgetary implications for the future, as the US cannot afford to continue on its existing track.
If passed, the reforms will deliver on Mr Obama’s top domestic priority by providing insurance to some 32 million of the Americans who currently lack coverage.
The House of Representatives and the Senate adopted different versions of the bill in November and December.
The usual procedure would be for two versions of legislation to be combined into a single bill for President Obama to sign into law.
But after Senate Democrats lost the 60-seat majority required to defeat a filibuster by Republicans, Democratic leaders decided to use a controversial procedure to ensure the bill’s passage.
Under the plan, the House will vote on a package of reconciliation “fixes” amending the Senate bill.
The Senate will then be able to make changes in a separate bill using a procedure known as reconciliation, which allows budget provisions to be approved with 51 votes – rather than the 60 needed to overcome blocking tactics.
According to Congressional Budget Office, the final version of the Democrats’ healthcare plan will cut the federal deficit by $138bn over 10 years.
The non-partisan body said the proposed legislation would cost about $940bn over a decade.
The reforms would increase insurance coverage through tax credits for the middle class and expansion of the Medicaid programme for the poor.
If approved, they would represent the biggest change in the US healthcare system since the creation in the 1960s of Medicare, the government-run scheme for Americans aged 65 or over.