His work was very good before he went to ISU.
That drop towards the time he was going for tenure is not a good sign. A university looks at your contributions there for a sign of future contributions, and he looked like he'd eventually stop publishing if granted tenure.
Another problem is the claim of 91% of tenures getting approved at ISU. True, but in his department the tenure rate was only 66%. Given his record, it's easy to see how he would get passed over for tenure in favor of others.
He kept his ID work out of the classroom.
And he wasn't denied tenure for that. But if you'll notice the chart, it looks like he started putting all of his work into the book instead of scientific publications that could get him tenure. He wasn't even first author on anything for three straight years.
I have heard a lot of complaints about the tenure system in general, how it concentrates too much on publication and doesn't necessarily look at the whole individual. Those are valid complaints. But the fact is that he knew the criteria and didn't fulfill them. He was even warned about his lack of research grants. Universities to a moderate extent operate off the money from such grants, so they push professors to pull in as much as possible. He was far below the average. Not good for tenure either.
In this whole picture I can't see anything but a whiner who couldn't cut it so he pulled the ID card. IMHO such people are just as slimy as those who pull the race card.