Realistically what the United States really needs isn't high speed rail but just passenger rail service. Standard speed mainline passenger service to more places and with more frequency than three times a week at 3am (which I wish was an exaggeration)

If I were totalitarian dictator of the US I'd first have the federal government sieze control of the entire rail network, including all dispatching and all of the private rail maintaince companies and lease trackage rights back to the railroads, keeping rail construction, dispatching and maintenance in house. Next I would create a true national passenger rail network, restoring service to every city possible that still has active right of way. Then, I would use my ownership of the rail network to force the class 1 railroads to construct and operate their trains in a manner condusive to actually moving freight and not blocking other trains (it's incredible how railroad company executives seem to hate railroads and do everything they can to avoid operating a functioning railroad) plus open up the rail network to new private freight and passenger companies, and finally I'd build new rail coordidors first following the existing interstate network and as those new rail coordidors bed in I'd start reducing lanes on the interstate and introducing tolls to further discourage the use of private vehicles. Maybe some would be converted into bikeways, maybe some would be re-greened. It would be a decision made on a case by case basis what to do with all of the space reclaimed by the highway network

We used to dream big and our governments used to undertake projects like this to improve our countries. And despite our governments being richer than ever they choose to stagnate and not take risks on big public projects like this