Some of our railway routes are the oldest in the world. Tunnels and bridges weren't built with the consideration of overhead electrification. So what do you do?
Electrify the parts you can and have trains that can run without external supply for the bits you can't electrify.
The international legion is made up of people from around the world, not just the US. It's not under US command. US civilians can act as they wish. Their actions are not the actions of their country.
The story you link is Biden relaxing US corporations taking up supply and support contracts. The article even says that these organisations will NOT be fighting, yet you willfully misinterpret it.
The USA, the country, is not in Ukraine.