This is Reform #1 in a three-part series on how to make all our votes count equally.
According to the Constitution, each state chooses delegates (electors) who then vote for the President. Except in Maine and Nebraska, these delegates are chosen on a winner-take-all basis. This system creates swing states, which get more attention (and more electoral power) than other states. To the candidates, votes in those states are worth more.
The simpler popular vote system would make each vote equal, but it's hard to move from the electoral college system to the popular vote system. Splitting votes like Maine and Nebraska do makes those states even less important to candidates, so I can see why states are reluctant to do that. Instead, some states have made a pact to deliver all their electoral votes to the winner of the national popular vote, even if that person didn't win that state's popular vote. This will only go into effect when enough states have joined to represent a controlling majority of electoral votes. So the pact needs 270 electoral votes; it currently has 132, from eight states and the District of Columbia.