WASHINGTON (AP) – Until six weeks ago, defenders of the Affordable Care Act could take comfort in some simple math. Five Supreme Court justices who had twice preserved the Obama-era health care law remained on the bench and seemed unlikely votes to dismantle it. But Justice Ruth Bader Ginsburg’s death and her replacement by Amy Coney Barrett have altered the equation as the court prepares to hear arguments Tuesday in the third major legal challenge to the law. Republican attorneys general in 18 states, backed by the Trump administration, are arguing that the whole law should be struck down. Invalidating the entire law would threaten coverage for more than 23 million people.