After a narrow vote to open debate on repealing the Affordable Health Care Act, commonly known as Obamacare, the United States Senate is set for a bruising battle over the future of America's healthcare system.
The deep divisions over the issue were demonstrated barely hours later on Tuesday when the Republican Party's most comprehensive plan to replace Obamacare came up well short of the votes needed to pass, failing by 43 to 57.
The proposal was the first of dozens - with potentially hundreds of individual amendments - that the Republicans intend to table for voting in sessions that could last well into the nights this week.
Earlier on Tuesday, the party had won by 50-51 a vote to begin the debate. Though Republicans have 52 seats, two of their senators - Ms Lisa Murkowski of Alaska and Ms Susan Collins of Maine - voted "no", leaving Vice-President Mike Pence to break the tie.
That prompted President Donald Trump to take to Twitter to berate Ms Murkowski, writing that she "really let the Republicans, and our country, down... Too bad!"
On Tuesday night, he told a roaring, placard-waving crowd at a rally in Youngstown, Ohio: "Any senator who votes against repeal and replace is telling America they are fine with the Obamacare nightmare, and I predict they'll have a lot of problems."
Insurance premiums for Obamacare have risen, but critics say whatever has been proposed by the Republicans will only make things worse, especially for the poor and those with pre-existing medical conditions. The Congressional Budget Office has estimated that one Republican proposal would leave up to 22 million more uninsured Americans by 2026.
"The vote to proceed on the 'healthcare' Bill is a step towards passing the most dangerous and destructive legislation in our modern history," Senator Bernie Sanders tweeted soon after the ballot.
Even Republican stalwart Senator John McCain, recently diagnosed with brain cancer and returning dramatically to Washington just to vote "yes" to open the debate, warned that he would not support the healthcare Bill in its current form.
Senate Majority Leader Mitch McConnell told reporters: "There will be a lot of different amendments offered by different members trying to craft the Bill. It's really entirely impossible to predict… exactly what amendments will be offered or what amendments will succeed. It's wide open."
At the core of the struggle is America's free-market approach to healthcare. Democrats - while still advocating a free market - lean towards a more socialised health system.
Republicans, however, want to reduce the federal deficit by passing more of the burden to states and individuals. The Democrats charge that Republicans are trying to lower the taxes on the rich.
Late Tuesday evening, on the steps of the Capitol, Democratic Party senators addressed an agitated crowd protesting against the repeal of Obamacare. "This is a handful of billionaires who want to do an ideological experiment on millions of Americans," Democrat Senator Sheldon Whitehouse said.
Democrat Senator Maggie Hassan said: "Every house must have access to healthcare. We need to keep fighting, what's at stake here is whether we are going to live up to that ideal that everybody matters."
Obamacare mandates health insurance and prohibits insurance companies from denying coverage to those with pre-existing medical conditions. The Republican plans weaken this, leaving people with pre-existing conditions vulnerable to being left with no or extremely expensive insurance premiums.