How do Trump's actions threaten the separation of powers ?

In each of these cases, President Donald Trump is attempting to block the examination of his conduct, by claiming that the chief executive is immune from various forms of investigation. At stake in these cases is the public’s ability to know about, and seek accountability for, misconduct.  More important, they represent a gut check for our system of separation of powers.

c

explanation:

the doctrine of nullification recommended that states living inside the union have the one-sided, inalienable ideal to void any law made by the national government that could be esteemed illegal.

the united states was shaped based on a general agreement among its individual states. hence, it is inferred that under the hypothesis of invalidation, since the states are the establishment of the union, they have the ability to referee and disprove unlawful laws.