A Supreme Court ruling against President Obama’s landmark health care law could prompt challenges to the Massachusetts law that inspired it, according to legal experts and activists following the case. The tenor and aggressiveness of the justices’ questions during three days of oral arguments on the federal law have caused some legal experts to predict the nation’s highest court could strike down the individual mandate - if not the entire law. If that happens, observers say, the ruling would likely encourage a lawsuit in Massachusetts court, or embolden organizers of a ballot initiative to repeal the state’s individual mandate.