A great soft target is electricity grid. The timelines for manufacturing large transformers for example can be many months and they usually don't have as much redundancy as you would expect. A semi coordinated attack against the grid, using dynamite to take out a number of pylons along main HV lines, easily accessible because they're out in rural areas. Combine with a number of sticks thrown over fences at transformers. And you could massively impact the US economy for months.