Harder than laying rail lines that already exist? Yes. Why wouldn’t it be?
What do you think is harder, leveling, elevating, compacting, laying down ties, and then laying and welding kilometers of the rail…or you just digging a hole every 200 yards and hanging wire?
We are already doing things a lot more difficult by simply laying down track, electrifying it isn’t going to be a problem. If the Russians could electrify rail all the way to the Pacific +50 years ago, I think we can manage.
do all new tracks also need to be built?
No, you could hang wire relatively easily and cheaply. But electrifying the rail would be the best solution. Something you could easily do while doing track maintenance over time.
The rails we utilize have to be regularly replaced anyways, we aren’t running on the same track we laid down a hundred years ago.
This is not a difficult material problem, this is how the majority of large nations handle mass transportation. America is just more concerned with protecting their car and airplane industry than they care about logistics or about solving climate change.