No. The US was never a democracy. It was organized as a federated republic. Each State is a republic, and the federal government is also a republic.
A republic is government by law (in other words, a constitution). That constitution defines each of the representatives, what power and authority they have, their term of office and it's jurisdiction, and the procedure for how they are each elected.
A constitution may only be modified by the owners of that document. For the federal constitution that means the States. For each of the State constitutions, that means the people of that State. A constitution may not be modifiable by the entity that the constitution creates (or it's not a constitution).
Some offices in the U.S., such as a Representative in the House, are elected by popular vote of the people in that district. That is specified in the Constitution. That does NOT make it a democracy. That constitution creates that office, the power and authority it has, it's length of term, and the method of electing that representative.
Democracies have no representatives and no constitution. Everything is by popular vote.