WASHINGTON — The Supreme Court sent a clear message Thursday that President Barack Obama's health care overhaul is here to stay, rejecting a major challenge that would have imperiled the landmark law and health insurance for millions of Americans. Whether you call it the Affordable Care Act, Obamacare, or in the words of a dissenting justice, SCOTUScare, Obama's signature domestic achievement is, as the president himself put it, "reality." The 6-3 ruling, which upheld financial aid to millions of low- and middle-income Americans to help pay for insurance premiums regardless of where they live, was the second major victory in three years for Obama in politically charged Supreme Court tests of the law.