I haven't read the whole thing, but they're only using Gallup's data up to 2015? So what if 2016 data tells a completely different story?
If you look at Ohio, Michigan, Wisconsin, Pennsylvania, and North Carolina, you have negatives for 2015 (using Huff posts averages)
June 2015
Ohio: -9.5
Michigan: -1.7
Pennsylvania: -10.4
North Carolina: -8.2
Wisconsin: +0.8 (August 2015)
All similar to Gallup's dismal marks. But when you look at this year:
October 2016
Ohio: +1
Michigan: +3.7 (November 2016)
Pennsylvania: +5
North Carolina: +2
Wisconsin: +8.3
Obama was in the positive territory near the election. These numbers wouldn't suggest that Democrats were losing those states (if we're basing it off of Obama's job approval)
BTW,
here's the link I used (I just changed the name of the state in the link to get the different state polls)