Republican politicians have campaigned on repealing President Barack Obama's healthcare reforms pretty much since they were enacted in 2010.
Now, with a governing majority, they've had to come up with a replacement plan - a task that has proved much more challenging than they may have imagined.
The latest bill, crafted by Republican Senators Lindsey Graham of South Carolina and Bill Cassidy of Louisiana, provides considerable discretion to individual states to craft their own healthcare systems, with financial support from the federal government.
Here's a look at some key differences between the existing law, informally known as Obamacare, and the Graham-Cassidy legislation. It is unlikely there will be government numbers on the impact before the bill comes to a vote.
Obamacare: All Americans are required to have health insurance or pay a tax penalty.
Republican plan: The mandate and penalty are repealed under the Senate plan.
Obamacare: Companies with more than 50 employees are required to offer health insurance or pay a penalty.
Republican plan: The mandate and penalty are repealed.
Obamacare: Raised Medicare taxes on the wealthy and imposed new taxes on medical devices, health insurers, drug companies, investment income, tanning salons and high-end health insurance plans.
Republican plan: Maintains roughly 90% of Obamacare taxes, including the tax on high-income earners, but ends the 2.3% sales tax on medical devices.
Insurance for dependents under 26
Obamacare: Requires insurers to allow children under age 26 to be covered by their parents' policies
Republican plan: Maintains this requirement.
Essential health benefits
Obamacare: Requires all insurance plans to cover certain health conditions and services, such as emergency room visits, maternity and postnatal care, cancer treatment, annual physical exams, prescription drug costs and mental health counselling.
Republican plan: States may apply for waivers that allow them to end mandatory coverage of certain health conditions, such as vision and dental care for children, hospital care, and outpatient services. States that receive such waivers could allow insurers to set a maximum amount they will pay for an individual's medical services - a practice that Obamacare had prohibited.
Pre-existing condition coverage
Obamacare: Prohibits insurers from denying coverage or charging more to individuals who have pre-existing medical conditions.
Republican plan: Gives states the ability to opt-out of requirements that insurers charge the same premiums for healthy and sick customers.
Obamacare: Expanded Medicaid health insurance for the poor to cover more low-income individuals.
Republican plan: Starting in 2020 it distributes money the federal government currently spends on Medicaid to states in the form of "block grants" that are capped based on a state's population and whose growth is limited. The money could then be used for a variety of health-related programmes, and not just for expanding coverage or assisting individuals with insurance premiums. According to independent studies, 34 states would see reduced government support for Medicaid and tax subsidies for individual purchasing health insurance, dropping federal outlays on Medicare by $175bn from 2020 to 2026.
States that agreed to expand their Medicaid coverage under Obamacare would be hit the hardest, as their additional funding would be phased out. In 2027 all federal block-grant funding would have to be re-authorised by Congress or it would end. States could impose a work requirement for individuals on Medicaid, although the disabled and pregnant women would be exempted.
Obamacare: Insurance companies prohibited from charging women more than men for the same health plan and must provide core services including maternity care and contraceptives.
Republican plan: Insurance companies prohibited from charging women more for health insurance, but states could apply for waivers that allow them to drop coverage for maternity care and contraceptives. The bill also bans women from using government money to buy plans that covers abortion and ends non-abortion Medicaid reimbursement to Planned Parenthood, a non-profit group that provides abortion services in some of its clinics, for one year
Obamacare: Insurers can charge older Americans no more than three times the cost for younger Americans
Republican plan: States can receive waivers to allow them to charge older Americans more.
Obamacare: Provided refundable tax credits for low-income individuals who purchased their insurance on government-run marketplaces and support for some out-of-pocket medical expenses.
Republican plan: Allows states to devise their own insurance subsidy plans. It expands the contribution limits on tax-free health savings accounts and allows individuals to use them for insurance premiums as well as out-of-pocket healthcare expenses and insurance co-payments.