But clearly this isn't politically predictive, since the new governor of that state is Larry Hogan (R), not Anthony Brown (D). What the Gallup data is instead particularly good at is showing trends over time.
Since the dawn of the Obama era, the whole country has shifted to the right. Literally every state but one is now more Republican it was than six years ago. (Which one? Be patient.) We colored the lines according to how strongly Democratic or Republican the states are now; note that red lines (Republican states in 2014) drift across the halfway mark into Democratic territory as you go back in time.
Another, perhaps easier way to see it is in an animation.
There are some special cases worth calling out. The state that has moved the furthest to the right since 2008 is Montana. The only state to move to the left? Alaska -- certainly thanks in part to the partisanship engendered by having a native daughter on the 2008 ballot. The state that has been most consistently Democratic is Rhode Island; the most consistently Republican, Wyoming.
Again, this doesn't tell us everything about what will happen in the polling booth. If you compare the Gallup partisanship breakdown to the 2012 election results, more Democratic states largely voted more heavily for Romney. But six states bucked that trend, going for the candidate of the "wrong" party.
But then, the case we used at the outset should make that pretty clear. Just ask Martha Coakley if she thinks Massachusetts voters can always be counted on to vote blue.