Stephen S. answered 09/20/23
Reading and Writing Specialist: phonics, ESL, essays, and SATs
Hi Lesya -- I think the principles your question refers to are Federalism and the Separation of Powers.
According to the US Constitution, Article X, "The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people." This allows states to make laws that are different from Federal (national) laws where the Constitution does not reserve those powers to the Congress.
Article II of the Constitution grants the president the power to enforce the laws Congress has passed, and that power, in recent decades especially, has taken the form of executive orders. This shows that the president has the role of executive (executing the laws), while Congress retains the power to write them (legislative).
I hope this helps!