"Hence, they believe the Act as a whole is invalid", Justice Stephen Breyer said in the opinion of the court.
"Yet", he added, "seven justices chose to avoid the question of the constitutionality by limiting its decision to a ruling on standing".
The lawsuit was led by a collection of red states that argued the ACA became unconstitutional when the 2017 tax law rendered the individual mandate penalty to zero. "Today's U.S. Supreme Court decision is a major victory for all Americans benefiting from this groundbreaking and life-changing law".
With three major challenges to Obamacare now having been resolved by the justices, Mr Biden added, "it is time to move forward and keeping building on this landmark law".
For Medicare recipients, "Obamacare" also improved preventive care, and more importantly, closed a prescription drug coverage gap of several thousand dollars that was known as the "doughnut hole".
Republican lawmakers said the "ruling does not change the fact that Obamacare failed to meet its promises and is hurting hard-working American families".
Texas Attorney General Ken Paxton, a Republican who led the challenge, vowed to continue to fight Obamacare.More news: UK, Australia agree post-Brexit trade deal
Those plaintiffs were 18 Republican-run states, later joined by two individuals, who claimed that if you cover one eye and hold the ACA up to the light while turning it counterclockwise, it will appear to be unconstitutional.
The law was Democratic former President Barack Obama's signature domestic policy achievement.
Former US President Barack Obama.
Because it dismissed the case for the plaintiff's lack of legal standing - the ability to sue - the court didn't actually rule on whether the individual mandate is unconstitutional now that there is no penalty for forgoing insurance.
After Texas and other states sued, a coalition of 20 states including Democratic-governed California and NY and the Democratic-controlled House of Representatives intervened in the case to try to preserve Obamacare after Trump refused to defend the law.
Reasoning that "the ACA imposes many burdensome obligations on States in their capacity as employers" and that "e$3 ven $1 in harm is enough to support standing", Alito questions the consistency of the majority's ruling. Justice Alito called the decision an example of "judicial inventiveness" and labelled the individual mandate "clearly unconstitutional".More news: Bidens to have tea with Queen Elizabeth as G7 ends
The closest Republicans got was in the summer of 2017, when they controlled both the House and the Senate and had President Donald Trump in the White House.
President Joe Biden's administration in February urged the Supreme Court to uphold Obamacare, reversing the position taken by the government under Trump, who left office in January. Justices Brett Kavanaugh and Amy Coney Barrett sided with the majority, while Gorsuch was the lone Trump-appointed justice that dissented. The states claimed they had an indirect injury in that the ACA caused increased use of state-operated medical insurance programs and caused increased administrative expenses.
House Speaker Nancy Pelosi, a Democrat, called the ruling a "victory for Democrats' work to defend protections for people with pre-existing conditions against Republicans' relentless efforts to dismantle them". Our AMA is committed to working with Congress and the Biden administration to achieve further advancements, such as making cost-sharing help more generous and available to more people, providing a coverage pathway to residents in states that have not expanded Medicaid who qualify for neither Medicaid nor ACA marketplace coverage, and fixing the ACA's "family glitch". He and other Democrats had criticized Republican efforts to strike down the law at a time when the USA was grappling with a deadly coronavirus pandemic.
"At no point in today's decision do the Supreme Court justices address the merits of our argument that ObamaCare is unconstitutional", said Arkansas Attorney General Leslie Rutledge.
Opposition to Obamacare seems to have receded as a political issue for Republicans as the party has emphasized other matters such as immigration, voting restrictions and hot-button cultural issues.
The Republican-led Congress cut the tax penalty for those who lacked insurance to zero as part of the year-end tax overhaul.
In 2012, Chief Justice John Roberts joined the four liberal justices on the court at the time, NFIB v. Sebelius, for a 5-4 decision that upheld the constitutionality of the individual mandate by deeming it a tax.More news: Florida shooting: Three dead, including shooter, at Publix supermarket