The legal fate of President Barack Obama's signature healthcare law will likely come down to two Republican appointees on the U.S. Supreme Court -- Chief Justice John Roberts and Justice Anthony Kennedy. That would be a familiar role for Kennedy, a moderate conservative who often has cast the decisive vote on the most contentious issues before the nine-member high court divided between conservative and liberal factions. A Supreme Court ruling on the healthcare law, adopted by a Democratic-controlled Congress after a bruising political battle, could be a defining moment for Roberts, who was named chief justice in 2005 by Republican President George W. Bush. "Given the deep ideological divisions over the case and the lack of precedent clearly on point, the court could easily rule either way," Ilya Somin, associate law professor at George Mason University, wrote in a recent blog post. U.S. appeals courts have issued conflicting rulings on whether Congress exceeded its power under the Constitution when, in adopting the healthcare law in 2010, it required that Americans buy insurance or face a penalty.