The Constitution specifically forbids the spending of any money from the Treasury of the United States unless the expenditure is authorized by a law passed by Congress. Congress has never authorized any Obamacare subsides, and a federal court has ruled them unconstitutional. President Trump has ordered that no further unconstitutional payments be made. The whining by the Democrats in Congress and with media bylines is interesting to watch.
The President sure is unpredictable. Why, the next thing you know, the President might do something like start acting as if treaties have to be ratified by the Senate.