As the OP pointed out, the problem is political and social, not technical.
And well...that's PLENTY enough to derail any efforts in the US.
You start mass eminent domain cases taking land from people and cities and well, you're gonna easily have 50+ years alone before the majority of those are settled one way or another.
Also, unless you get long straight shots of track...you're not going to have true High Speed Rail....and part of the obsticals for that is having to stop many times in many cities, turning to go to each one of those.....and if you don't do that and don't have service to many spots along the way.....those cities and states and localities aren't going to go out of their way to help take away land just to have something go speeding by them and be of no use to them there...
And if you can't really get true High Speed rail in.....most of the US will do "so, why bother? We already have highways, cars and planes to travel long distances fast...why do through the huge expense, litigation and hassle of doing rail?
There would be little perceived ROI to the average US citizen.
I mean, why would someone in Iowa give a flying fuck if someone in NYC could ride a fast train to LA?