America’s Founders built our system of government with State Rights and Citizen Rights to elect Federal Legislators. “Separation of Powers” was included to balance control between the Federal Executive, Legislative and Judicial. Their model was a Democratic Republic, not a Democracy with majority rule.
The current Executive Election has Popular Vote and Electoral College. The Electoral College ensures representation for all States equally instead of allowing the most populous States to control America (i.e. permit California, New York, Pennsylvania and Illinois to Elect every US President).
The current Legislative Election includes US House (Popular Vote) and US Senate (Popular Vote). The US Senate popular vote began in 1913 (Amendment 17). Originally, US Senators were appointed by the State Senates (similar to the Electoral College). The State Senates would vote on which 2 people to send to Washington every 6-years.
The change in 1913 meant both branches of the Federal Legislature would be elected by popular vote, which eliminated State Rights for the US Senate AND permits high-population areas to elect statewide US Senators (e.g. In California: San Francisco, Los Angeles and San Diego control US Senate elections).