Obamacare v Republican plan compared
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.
Here's a look at some key differences between the existing law, informally known as Obamacare, and the Better Care Reconciliation Act, which has been unveiled by Republican senators.
The Senate bill reflects most of the elements that were in a bill already passed by the House of Representatives, with a few changes.
Obamacare: All Americans are required to have health insurance or pay a tax penalty.
Republican plan: The mandate is repealed, but individuals who forgo health insurance for more than 63 days must pay a 30% surcharge on their insurance premiums for a year.
Obamacare: Companies with more than 50 employees are required to offer health insurance or pay a penalty.
Republican plan: This mandate is repealed.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: Repeals most Obamacare taxes and delays implementation of the tax on high-end health insurance plans to 2026.
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, cancer treatment, annual physical exams, prescription drug costs and mental health counselling.
Republican plan: Allows states to define what benefits are mandated, or opt out of the requirement entirely.
Pre-existing condition coverage
Obamacare: Prohibits insurers from denying coverage or charging more to individuals who have pre-existing medical conditions.
Republican plan: States can let insurers charge as much as they like to sick people. Allocates $8bn to help subsidise those patients.
Obamacare: Expanded Medicaid health insurance for the poor to cover more low-income individuals.
Republican plan: Phases out Medicaid expansion to reduce federal funding on the programme over the next decade. The CBO has yet to score how much the government would save - the House bill saved more than $800bn in 10 years, and the Senate bill makes even sharper cuts.
Also gives states greater flexibility in administering the programme in exchange for fixed federal spending.
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 still banned from charging women more, but states could allow insurers to drop maternity care and contraceptives from basic benefits. Also bans women from using federal tax credits to buy a plan that covers abortion.
Obamacare: Insurers can charge older Americans no more than three times the cost for younger Americans
Republican plan: Insurers can charge older Americans five times as much as younger Americans. States would also be able to set their own ratio.
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: Alters formula for tax credits, which will expand the benefit to more middle-class Americans but probably raise the costs for some elderly and less-affluent individuals.