This is a breakdown of how Americans are affiliated with the Republican and Democrat parties or as independent. The largest group in the United States are Independent voters
Facts Not Opinions uses the top national polls provided by RealClear Politics, direct access provided in the link in graph title. Their website provided the ability to drill down further and see candidates at the state and national level including those outside the Republican and Democrat parties.
"Established in Article II, Section 1 of the U.S. Constitution, the Electoral College is the formal body which elects the President and Vice President of the United States. Each state has as many "electors" in the Electoral College as it has Representatives and Senators in the United States Congress, and the District of Columbia has three electors. When voters go to the polls in a Presidential election, they actually are voting for the slate of electors vowing to cast their ballots for that ticket in the Electoral College."