Attorneys general in several states, including California, Connecticut, Kentucky, Massachusetts and New York, who said they planned to sue the Trump administration to keep the money flowing need to go back to law school to study the Constitution.  The President has absolutely no authority to spend money not appropriated by Congress.  Although Obamacare authorizes the subsidies, money to pay the subsidies has not been appropriated by Congress.  Thus, it is illegal for the Trump administration to pay them.  The only reason I can think of for the AGs wanting Trump to make the illegal payments is so they can then demand his impeachment.