As governor of Massachusetts, Mitt Romney signed into law health-care rules that required his constituents to obtain health insurance, much as ObamaCare does.

Richard A. Bloom/Corbis

he future of President Obama's health-care overhaul now rests in the hands of the Supreme Court. And many legal experts predict that the court's conservative majority will kill the Affordable Care Act by declaring its linchpin, the individual mandate (the requirement that virtually all Americans buy health insurance), unconstitutional. Liberals find that prospect galling, especially since, as they assert, the mandate was "originally a conservative idea." Is that true? Here's what you should know:

Who came up with the idea?
Conservative economists developed the concept in the late 1980s, when they were searching for a market-based alternative to the government-sponsored, universal health-care system liberals were proposing. Mark Pauly, a professor at the University of Pennsylvania's Wharton School of Business, suggested offering tax credits to help everyone buy at least minimal "catastrophic" insurance, and he proposed making it mandatory to get coverage. The conservative Heritage Foundation latched onto the idea, and pitched it to Republicans in Congress.

And did Republican leaders support it?
Some did, and when President Bill Clinton started pushing his failed health-care reform plan in the 1990s, the GOP presented the Heritage Foundation approach as an alternative. Twenty Republican co-sponsors supported a Senate bill that formally proposed the individual mandate, but the idea faded when Clinton's effort failed. In 2004, Mitt Romney, then governor of Massachusetts, revived the idea as part of a health-care overhaul for his state, which he signed into law in 2006. Romney, the GOP frontrunner for the 2012 election, is now vowing that, if elected president, he'll scrap Obama's federal version of the mandate.

Why have Republicans turned on the idea?
Out of political expedience, according to critics. Until ObamaCare came along, says David Frum at The Daily Beast, conservatives insisted the idea was "the secret to a well-functioning national health-care system." Now some of those same people claim "a health-care mandate is tantamount to the extinction of economic freedom" because it's convenient to say so. Still, let's not overstate the individual mandate's conservative roots, says Ramesh Ponnuru at National Review. A minority of think-tank types have always liked the idea, and some Republicans embraced it when they were forced to find an alternative to "HillaryCare." But this was never part of the GOP platform. 

Sources: Daily Beast, National Review, Outside the Beltway, Policymic, Washington Post