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In one of its most controversial decisions, the Supreme Court in 2012 upheld the constitutionality of a provision in the Affordable Care Act (ACA) mandating individuals purchase qualifying health insurance or else pay a fine, with Chief Justice John Roberts casting the deciding vote in favor of the law. However, nearly six years later, a provision included in the Tax Cuts and Jobs Act, passed mostly along party lines in December 2017, may soon force Roberts to reevaluate his decision, potentially ending the health care law without a single vote being cast in Congress.

In Roberts’ majority opinion, which saved the ACA from what appeared to be its certain death, he reasoned the federal government has the authority to impose an individual health care mandate because, despite language in the ACA calling the mandate a penalty, it’s effectively a tax and Congress has the constitutional authority to impose taxes. (Currently, those who fail to purchase a “qualifying” health insurance plan are subject to a penalty of $695 per adult, up to a family maximum of $2,085, or 2.5 percent of income, whichever is greater.)

Interestingly, Roberts joined the Supreme Court’s more conservative justices in rejecting the primary argument made by the Obama administration and the liberal justices, who claimed the federal government has the authority to impose a mandate to purchase health insurance under the Constitution’s “commerce clause” — a provision granting to Congress the power to “regulate Commerce with foreign Nations, and among the several States, and with the Indian Tribes.”

Roberts’ claim that the individual mandate is a tax was controversial, to say the least, but it may have opened the door to the law’s ultimate demise in a surprising way: If the individual mandate is only constitutional because it’s a tax, then the removal of the penalty from the law should gut the mandate of its constitutionality. And that’s precisely what happened in December, when Congress passed the Tax Cuts and Jobs Act.

One of the provisions included in Republicans’ tax reform bill will end the monetary penalty imposed by Obamacare in January 2019 without ending the mandate to purchase health insurance — something Congress likely couldn’t have done under the budget reconciliation rules used to pass the tax bill. By removing the Obamacare fine — or, according to Roberts, the “tax” — the Affordable Care Act likely became, or will become, unconstitutional under the opinion issued by Roberts and the dissent published by four other justices in the 2012 case.

The reason the entire health care law could be determined unconstitutional if the individual mandate is struck down is that the Supreme Court has determined in previous cases that when a single provision of a law is ruled unconstitutional and it’s clear Congress wouldn’t have passed the bill without that provision, the entire law must also be thrown out.

Former Justice Antonin Scalia explained this precedence in the dissent he authored in the 2012 case that upheld Obamacare’s constitutionality, writing, “even if the remaining provisions can operate as Congress designed them to operate, the Court must determine if Congress would have enacted them standing alone and without the unconstitutional portion. If Congress would not, those provisions, too, must be invalidated.”

Because Congress itself declared the individual mandate was “essential” to the entire law’s operation when the Affordable Care Act was passed, a reasonable case could be made that Congress would never have passed the ACA without the individual mandate, and thus the Supreme Court should strike down the entire law if it rules the mandate unconstitutional.

This argument, which was first brought to our attention by former Virginia Attorney General Ken Cuccinelli, who was previously one of the leaders in the legal battle against Obamacare, is gaining traction and could soon result in yet another Obamacare showdown in the Supreme Court. On April 23, 20 states and several other plaintiffs filed suit in the U.S. District Court for the Northern District of Texas alleging the Obamacare individual mandate is now unconstitutional and that if the mandate is determined to be unconstitutional, the entire law must also be thrown out.

If forcing Americans to buy health insurance is “essential” to the ACA, then the unconstitutionality of that “essential” mandate could very well sink the entire health care law, accomplishing in an instant what the Republican-led Congress has failed to achieve since taking power following the 2016 elections.