Nigerian House of Rep vs President Buhari. 

The Charles-Louis Montesquieu Theory of Separation of Powers and Check and Balances is still intact. 

His Spirit of the Laws, according to NCSL is considered one of the great works in the history of political theory and jurisprudence, and it inspired the Declaration of the Rights of Man and the Constitution of the United States. Under his model, the political authority of the state is divided into legislative, executive, and judicial powers.

Separation of powers, therefore, refers to the division of government responsibilities into distinct branches to limit any one branch from exercising the core functions of another.  The intent is to prevent the concentration of power and provide for checks and balances.  

• The traditional characterizations of the powers of the branches of American government are:
• The legislative branch is responsible for enacting the laws of the state and appropriating the money necessary to operate the government. 
• The executive branch is responsible for implementing and administering the public policy enacted and funded by the legislative branch. 
• The judicial branch is responsible for interpreting the constitution and laws and applying their interpretations to controversies brought before it.

They are co-equal. And no one branch can compel the other branches to act. Therefore, the House of Rep can demand the attention of the President before it. And the President has the right to decline to appear before them.