Now with state-by-state winner-take-all laws (not mentioned in the U.S. Constitution, but since enacted by 48 states), presidential elections ignore 80% of states and voters.
They ignore 12 of the 13 lowest population states (3-4 electoral votes), that are non-competitive in presidential elections. 6 regularly vote Republican (AK, ID, MT, WY, ND, and SD), and 6 regularly vote Democratic (RI, DE, HI, VT, ME, and DC) in presidential elections. Voters in states that are reliably red or blue don't matter. Candidates ignore those states and the issues they care about most.
In 2008, of the 25 smallest states (with a total of 155 electoral votes), 18 received no attention at all from presidential campaigns after the conventions.