It’s important to know the distinction.
A system of government by the whole population or all the eligible members of a state, typically through elected representatives.
A state governed in such a way.
A Republic, by definition, has two principle elements. First, it is controlled by Law; therefore, it does not control Law. Second, it recognizes the private independent sovereign nature of each person (man or woman) of competent age and capacity; therefore, a Republic must be representative in its nature.
A Republic recognizes Law is unchangeable, or at least that it can only be changed by a higher source than government. In a Republic the concept of “collective sovereignty” cannot exist, except with recognition that the State or nation, as a body of sovereigns, can speak through one elected voice; though that one voice can never lawfully interfere with the private rights of the individual sovereigns.
“A Constitutional Republic” is a government created and controlled, at least, by the Law of a Constitution. The Constitution of the United States of America was, in Law, a foundation based on the Bible, the Magna Carta and the Declaration of Independence. Those documents recognize man’s sovereignty, the divine nature of man’s creation and man’s divine right to Life, Liberty, the means of acquiring and possessing Property, and the pursuit of happiness.