But here’s the rub: unless you analyze how each of these states has shifted over time, you’ll be throwing good money after bad and chasing states that have deliberately decided to shift hard to the left in favor of Democratic candidates. Without looking at how states have shifted relative to the national popular vote, there’s also the tendency to incorrectly assume that some states — like those that were barely lost by the GOP in 2000, yet drifted out of reach in 2012 — are no longer worth the effort.

Put another way: if a state voted for Gore by 3 but Obama by 6, the immediate thought is, “Dang, we lost another one.” But what if that state initially went to Gore by 2.5 points over his national win but delivered an even smaller margin of victory to Obama 12 years later? Despite the loss, that state would have actually drifted rightwards, not leftwards, compared to the country as a whole. Those states deserve the biggest efforts going forward, with voter contacts, registration drives, and advertisements designed to capitalize on the trend and eventually turn those states red.

There are also a number of states that have brought the GOP a great deal of frustration by turning against it. If the shift away from Republicans is small — say no more than 3.5 points — a serious counter-attack in these states could very well pay off and bring them back into striking distance, requiring additional investments and attention from the Democratic candidate, or the efforts could successfully push the states into the Republican column.