I think they, whoever "they" are, do not want to damage the grid if they cant easily repair it, its too valuable a tool.
They also dont want to damage any crops, they will need food after they win, if they win, the war. I think nukes are very unlikely except for use in bigger cities and govt agencies.
I heard on the news they did stop an IED trying to cross the border but they never explained the people bringing it over, where they were going or what their plans were. Also, why risk bringing one over the border when you could just make one here?