Titan II ICBM launch
Mark 6 re-entry vehicle
Doesn’t need to be that large. Some studies have found that a single bomb of 1.5 megaton about 200 miles over Kansas would effect the entire nation.
The launch vehicle is the hard part. Iran currently has the capability to put 65kg into this high of orbit.
Last week I read a very moving (fictional) account about the aftermath of an EMP attack on the US. The novel is called “One Second After”. It’s available an Amazon, but if you’re a cheap SOB (like me) you can also get it as a free PDF online. Just do a Google search for “one second after book PDF”. I was crying half the time I was reading it.