I don’t understand why a Hyperloop is the next logical step. Making a low pressure tube is probably pretty hard at scale.

Every design is trying to minimize air resistance. Why not wrap already existing high speed rail lines with a cheap air barrier then create a wind tunnel inside rather than a vacuum? If you could move air at a similar speed to the train you could achieve wind resistance that is effectively negligible or even negative.

Am I thinking about this wrong? Is the energy required to remove all air from a tube significantly lower than pushing air through the tube while a train moves?