Skills introduced in the lower grades can be acquired by most everybody, and that is where Bush is. Levels attained do correlate with IQ, and you say, but that does not absolve primary schools from teaching normal children to read and calculate. I did not kmnow the 85 number for HS grad, but I do know that college grad is 120.
No the data for ability to graduate from an academically oriented college goes down to IQ of 110 or 20% of the population. Minnesota now graduates 28% after five years and including community colleges.
An IQ of 125 or better occurs in only 5% of White Europeans.
At 125 or above you can do most professions--law, medicine, Phd, Combat aircraft commander and so forth. Down from 125 there is a continuum. Surely, hard work and coaching can help overcome some degree of limitation, but in the end the destiny of most of us is what we are born with is what we do with.
These figures are well known to psychologists but seldom are quoted or used in policy planning because everyone secretly believes they and their cohort "are all better than equal" a la Prairie Home Companion and Garrison Keillor.