President Barack Obama\'s overhaul of the U.S. health care system - the key legislative achievement of his term - could be gutted, crushed or left standing Thursday when the conservative-dominated Supreme Court rules on the constitutionality of the sweeping law in the heat of the presidential election campaign. The momentous and politically charged high court ruling will affect Obama\'s bid for a second term regardless of what the nine-justice panel decides. A decision to strike down the law, which has wide support among progressives in Obama\'s base of support, could energize those voters and boost turnout for the president. If the law is allowed to stand, conservative Republicans might be more inclined to go to the polls, thereby helping Republican challenger Mitt Romney. Polls show a majority of Americans do not support the overhaul, which, ironically, was based on a plan put in place in Massachusetts when Romney was governor of the state. The Massachusetts law, however, is widely supported by residents in the state, where it has been effect since 2006. While Romney defends the plan he shepherded into law in the Northeastern state, he says such changes should be left to the individual states and not imposed by the federal government. Romney has joined his party in promising to revoke the health care overhaul. At a campaign even in Virginia on Tuesday, Romney said Obama\'s term would \"have been wasted on something that has not helped the American people\" should the court strike down the health care law. Were it upheld, Romney said, \"we are going to have to have a president, and I am that one, that is going to get rid of Obamacare and we are going to stop it on day one.\" Central to the challenges to the law, which variously have been upheld and rejected in lower courts, involves what is known as the individual mandate. That portion of the overhaul requires that all Americans obtain health insurance or face a federal fine. The mandate takes effect in 2014, at the same time that the law would prohibit insurance companies from denying coverage to people with existing health problems. Most experts say the coverage guarantee would balloon costs unless virtually all people joined the insurance pool. Opponents say Congress overstepped its constitutional authority by issuing the insurance mandate. The Obama administration says the requirement is permissible because it serves to regulate interstate commerce. Most people already are insured. The law provides subsidies to help uninsured middle-class households pay premiums and expands Medicaid, federal health care for poor people, to expand that program. The court could allow the federal law to stand as is or strike down individual provisions like the insurance coverage mandate. All outcomes short of finding the law fully constitutional would produce an upheaval in the health care sector that has been working toward implementation of the big changes already in place or coming into effect two years from now. Because the Affordable Care Act is so complicated, an orderly unwinding would prove difficult if it were overturned entirely or in part. Better Medicare prescription drug benefits, currently saving hundreds of dollars for older people with high drug costs, would be suspended. Medicare is low-cost government health care for Americans when they reach age 65. The same would go for full coverage for preventive care that is now available to retirees and working families alike. Partially overturning the law could leave hospitals, insurers and other service providers dealing with tax increases and spending cuts without the law\'s promise of more paying customers to offset losses. If the law is upheld, other complications could result. The nation is so divided politically that states led by Republican governors and legislatures are largely unprepared to carry out critical requirements such as creating insurance markets. While it\'s unclear how the justices will rule, oral arguments did not go well for the Obama administration, especially on the central issue of requiring all Americans have insurance. A mixed verdict from the high court would be the most confusing outcome. Some parts of the law would be struck down while others move forward. That kind of result would seem to call for Congress to step in and smooth any necessary adjustments. Yet partisan divisions are so intense that hardly anyone sees a chance that would happen this year.