If you ride them most of the people don't seem like train nerds. Properly done rail would be viable for most of the US. A cross-country trip not really. But anything from about 800 to 1200 miles could be competitive with commercial flights and have extrinsic benefits as well. A 1200 mile flight takes about 3 hours. Add in a minimum of one hour on each end for airport transit and moving about within the airport and your at 5 hours, and often times much more. High speed rail moving 200 mph with 6 to 8 stops may take a couple more hours in the most advantageous to air comparison. Also consider than many of those 6 to 8 stops would be serving places that may require connecting flights or where people are driving to the major airport from.

It has the potential to be nicer, safer, cheaper and more environmentally conscious. There's no good reason America doesn't have top tier rail transit.

There are plenty of locations in the US where fast intercity regional rail could easily be useful and work. Florida, Portland - Vancouver, Alabama/Georgia/Carolinas/Virginias, Midwest.

Yeah, few people will take a cross-country train outside of for the novelty and the attraction itself (which are still not to be dismissed), but that doesn't mean there aren't plenty of <4-5h trips that can be made via train if there was good, reliable and fast service.