Also on Monday, President Donald Trump said Republicans may wait for the federal insurance market to collapse ...

Presidential Oath of Office: "I do solemnly swear (or affirm) that I will faithfully execute the Office of President of the United States..."
Constitutional Duties of Office of President (Art 2, Sec 3): "[The President] shall take Care that the Laws be faithfully executed..."

As long as the ACA is the law Trump better take Care that it is faithfully executed, or be derelict of his oath of office. 

This man has no clue that he in his capacity of President is actually just an administrative civil servant most of the time. Do your job Trump.