Then it would be up to the Supreme Court to determine that the law was unconstitutional.
Our government is composed of three seperate but equal branches that operate under a system of checks and balances. It was designed that way for a reason, so that no one branch could usurp power.
I've seen quit a few leaks attributed to "senior White House officials " in the past.
All three branches are supposed to do so...as a matter of fact, the SCOTUS gives Congress and The Executive Branch the benefit of the doubt, and have ocassionally opined that they might consider not doing that in the future, as Congress clearly has been passing laws that they have not reviewed for Constitutionality.