<P> The act largely retains the existing structure of Medicare, Medicaid, and the employer market, but individual markets were radically overhauled around a three - legged scheme . Insurers in these markets are made to accept all applicants and charge the same rates regardless of pre-existing conditions or sex . To combat resultant adverse selection, the act mandates that individuals buy insurance and insurers cover a list of "essential health benefits". To help households between 100--400% of the Federal Poverty Line afford these compulsory policies, the law provides insurance premium subsidies . Other individual market changes include health marketplaces and risk adjustment programs . </P> <P> The act has also faced challenges and opposition . In 2009, Senator Ted Kennedy died, and the resultant special election cost the Democrats their 60 seat filibuster - proof Senate majority before the ACA had been fully passed by Congress . The Supreme Court ruled 5 to 4 in 2012 that states could choose not to participate in the ACA's Medicaid expansion, although it upheld the law as a whole . The federal health exchange, HealthCare.gov, initially faced major technical problems during its rollout in 2013 . In 2017, a unified Republican government failed to pass several different partial repeals of the ACA . The law spent several years opposed by a slim plurality of Americans polled, although its provisions were more popular than the law as a whole, and the law gained plurality support by 2017 . </P> <P> The ACA includes provisions to take effect between 2010 and 2020, although most took effect on January 1, 2014 . Few areas of the US health care system were left untouched, making it the most sweeping health care reform since the enactment of Medicare and Medicaid in 1965 . However, some areas were more affected than others . The individual insurance market was radically overhauled, and many of the law's regulations applied specifically to this market, while the structure of Medicare, Medicaid, and the employer market were largely retained . Most of the coverage gains were made through the expansion of Medicaid, and the biggest cost savings were made in Medicare . Some regulations applied to the employer market, and the law also made delivery system changes that affected most of the health care system . Not all provisions took full effect . Some were made discretionary, some were deferred, and others were repealed before implementation . </P> <P> Among the groups who remained uninsured were: </P>

When was the aca released to the public