The viable HSR network for the US looks roughly like this:
* Existing NEC (DC to Boston via Baltimore, Philly, NYC, Hartford/Springfield/Worcester or Providence)
* NYC to Montreal and Boston to Toronto, with an interchange at Albany
* Midwest star shape, centered at Chicago, with prongs to Minneapolis, St. Louis, Detroit, Cleveland, Louisville or Cincinnati. The southern Midwest region is kind of hard for me to crayon a network.
* (Not part of the US strictly speaking) Detroit to Quebec via Windsor, Toronto, Ottawa, Montreal. Basically all of Canada's population on one rail line, with easy access to the US via interchanges at three separate points.
* Hooking up the Midwest to the NEC, although I'm somewhat dubious of the viability here.
* Texas Triangle (Houston, Dallas, Austin, San Antonio)
* California: SF, San Jose, Sacramento, LA, San Diego, Las Vegas, Phoenix.
* Maybe viable: Portland-Seattle-Vancouver
* Maybe viable: SEHSR, from Miami to Atlanta, and thence to Midwest (via Nashville) or NEC (via North Carolina's Research Triangle and Richmond).
(Citation: this is largely based on Alon Levy's crayoning, found here: https://pedestrianobservations.com/2021/03/22/high-speed-rai...)