Depends on what you mean by most.

• most of the population is quite achievable. Send a little time at https://www.ushsr.com/
• most of the geography, trillions, and we couldn’t afford to keep it operating

I really think that confusing this is a common mistake. People claim high speed rail is impossible in the US because we’re big (and ignoring China, eu), but we have plenty of cities, and most of them are clustered. High speed rail is great for cities within a few hundred miles of each other. We got those, and that’s most of the population

It’s specious to take scenarios high speed rail doesn’t do well at and claiming that it means it can’t work. Let’s apply a little intelligence here’d and use the right technology for the right scenario