It won't be nukes. I can pretty much guarantee the first salvo will be cyber warfare.
I would say that foreign states have already breached many of our civilian infrastructure networks with nuclear plants being the rare exception.
The first salvo will probably be traffic signals for an entire region. A commute of an hour will the three with the traffic lights out. That would be absolute gridlock in the cities. Area that rely on mass transit will have those systems targeted so no more subways and inter-city/region rail. Air traffic control would be spared.
In this same opening salvo will be a hit on US SNAP / EBT (Food Stamps). I would go with a 75 / 25 split where some receipts get thousands of dollars to spend and others get nothing. Such, you get people grabbing cart loads of food while other get nothing, which is a really good way to start riots.
Keep on this track, I would hit food distribution warehouse computer system so they couldn't know what to bring where without a painstaking process.
Perhaps, cell phone transmitter could be targeted. The telecom system may have some security but what about all those back up generator. Maybe some run without control systems causing a fire.
This is just me typing this up on the shitter. Imagine what could happen with dedicated people. Your mother life would be so inconvenienced she would go crazy on the first salvo.