Why not use national head-to-head polls instead?
National polls have the advantage of being current—that is, people express their support for each candidate all at the same time. The state head-to-head polls suffer because some polls are older, and public opinion may have changed since the older polls were taken. But the national head-to-head polls have some disadvantages. Most importantly, they predict the outcome of a national popular vote. We don’t elect our presidents by popular vote. As we learned in 2000, the national popular vote doesn’t always give the same election outcome as the Electoral College vote.
