The US presidential electoral system is in effect a two-stage decision system. In the first stage, the voters from every state elect a certain number of members of electoral college, who are pledged, de facto if not de jure, to vote for a certain candidate. In the second stage, the electoral college elects the president.So in fact, everything happens as though the States of the Union elected the president, where each state receives a certain weight (fixed a priori), and votes according to the result of the popular vote in the state.