Question

How does the constitutions ensure no branch becomes too powerful?

Answer 1

They use a system called "Checks and Balances". 

Answer 2

By using a system of checks and balances. The Legislative Branch can impeach Supreme Court Justices, and the Executive Branch appoints them. The Judicial Branch can declare certain actions taken by the Executive Branch to be unconstitutional, and can declare laws made by the Legislative Branch unconstitutional. The Executive can veto laws made by the Legislative. The Legislative can impeach the president (Executive Branch). Does this make sense?