Compared to the House version, the Senate version of the bill expands tax credits to help offset the cost of buying insurance on marketplaces, but the credits are still below what's in the Affordable Care Act. It would repeal tax increases on higher-income people, medical companies and others that had financed expanded coverage.
With a majority of 52 senators, Mr McConnell can only afford to lose two Republican votes on the bill.
Speaking on the Senate floor, Mr Schumer asserted that the Senate's version would end Medicaid "as we know it" by cutting federal support for the programme even more than the House bill, which cut it by more than $800bn, he said. "Because Obamacare is a direct attack on the middle class, and American families deserve better than its failing status quo".
Without the votes of Democrats and the four Republicans who are withholding support, the measure will not pass the Senate.
Sen. Roger Wicker of MS expressed some disappointment that the new bill still resembles Obamacare in some aspects.
Many will be "looking to see if there are things that we can do to refine it, and make it more acceptable to more members in our conference, to get to 50", Senator John Thune said.
From higher deductibles to massive cuts to Medicaid to higher premiums for older Americans, the Senate bill will make life worse for patients from the minute it's enacted.
Some conservative and moderate GOP senators have their doubts, too. "I want to hear from my bosses, the people of Montana, about what they like and don't like about this legislation", Tester said.
The plan would also provide funding created to help stabilize the Obamacare insurance markets in the near term and funnel money through programs to cut off access to funding for abortion providers.
As of 2020, the bill also eliminates cost-sharing subsidies that help low-income Americans pay for their insurance. Obamacare's Medicaid expansion, which extended the program to those making 100% to 138% of the federal poverty limit, would be phased out over three years starting in 2020. Both measures would give states more flexibility over insurance markets, including allowing insurers to offer plans that don't cover essential services such as emergency visits, mental health, maternity care and substance abuse treatment.
Many insurance plans are already planning large premium hikes for the ObamaCare exchanges or are completely exiting the marketplaces next year amid growing uncertainty over the future of the law and mounting financial losses. But younger people would still get more generous subsidies than they do under current law.
"To say people will die under this law is not an exaggeration", Mike Oxford, an organizer for the group, said in a statement. Dean Heller of Nevada, facing a competitive 2018 re-election battle, Ohio's Rob Portman and Shelley Moore Capito of West Virginia expressed concerns about the bill's cuts to Medicaid and drug addiction efforts.
Many Republicans, including Paul, were left out of deliberations regarding the legislation, with party leaders holding several closed meetings over the past few weeks leading up to the reveal. Such a prohibition is a major demand by conservatives, but special rules the Senate is using to ease passage of the legislation restrict the policy changes the measure can include. That language could be forced out of the bill for procedural reasons, which would threaten support from conservatives, but Republicans would seek other ways to retain the restriction. Federal assistance will continue through 2019 to decrease costs for low-income Americans.
Senate leaders plan to move the bill to the floor after receiving an analysis from the nonpartisan Congressional Budget Office, which said Thursday it will do "early next week".