Trump going for a Bushie is a sign of consolidating power, and also extending an olive branch to the Bush wing of the party. Just not the Jeb Bush wing.
Trump is going to need allies, as all the people who brought him to the dance are gone.
The risk is that Bushies fill the (whole lot of) empty slots around the administration.
Who will co-opt whom first?
You are of course absolutely correct. This was a backroom deal. The Bush wing was consulted and knew it was coming. It was interesting that GW sent out his approval letter almost before Kavanaugh had finished his acceptance speech. These days it takes GW 3 days to figure out where to...
No matter who President Trump nominated the Democrats were going to scream like hell and do their best to drag this thing out to make sure that it is a midterm issue. But this nominee was a compromise and the Demwits know it. President Trump has good instincts and picked someone with a long track record that longtime DC Republicans would line up behind and Democrat swamp creatures would put up a mostly a show fight against.
So let the character assassination begin...