that Trump would use them as a foil for a military action in order to gain popular support for his remaining in power. The book also goes on to say that not only Gen. Milley, but also Def. Sec'y, Esper and AG Barr were deeply concerned about Trump's mental state after losing the election...so, this whole thing isn't just about Gen. Milley...lots of other people (incl. civilian leaders) were very concerned...my personal take is that Milley's call was no secret to them, or an even larger group in national leadership.
This is a bit more compelling than arguing about what grade to give Biden on the evacuation of Afghanis and a couple hundred conflicted dual-citizenship Afghani-Americans...at least to my mind it is.