What is the form of government of the United States?

Why this is the answer

In a republic the people hold the power and use it by electing representatives, instead of a king or queen ruling by birth. The American version has two extra words in its full name, and each one matters. It is constitution-based because a written Constitution says what the government may do and where its power stops. It is federal because power is shared between the national government and the fifty states. "Representative democracy" describes the same idea from the voter's side: you govern yourself through the people you elect to local, state and national office. Any of the three official answers is accepted. Memory hook: three answers, one idea. The people rule, through representatives, under a written Constitution.