According to this site
http://www.wisconsinproject.org/countries/pakistan/missiles.html
“Pakistan is capable of producing nuclear warheads approximately the size of a soccer ball and weighing 400 kg”
Maybe a little heavy for the conventional suitcase but certainly small enough to fit in one. I would presume the Soviet Union would have developed this technology long before Pakistan. So it appears that the “suitcase nuke” was technically possible; whether or not they were deployed in the U.S., I don’t know.
spoke-, wasn’t it in TIME a couple of issues ago?
I saw something similar, in the “## years ago” section at the beginning of the magazine. I think it was by Hugh Sidey, who covered the White House for TIME during the Kennedy period.
His version was that a group of trusted journalists was having a deep-background lunch with JFK (remember, pre-Watergate 
) and this topic came up. JFK said that the Soviets had a nuke in their embassy; Sidey said, “Yeah, sure.”
Kennedy went alpha-male, stared at Sidey, and said “I’ve been reliably informed that they do. Do you know something I don’t?”
JFK playing with journalists’ minds? JFK giving the journalists a glimpse of terror? JFK telling them the straight goods? who knows?
What should be looked at is how a nuclear explosion is created. After that question is answered it would be possible to speculate whether suitcase bomb is possible.