That still would have left the U.S. as one of the largest countries on the planet, and fallout would largely have dissipated after two to six weeks. Congress, the president, and the federal reserve agents would likely have survived thanks to top secret bunkers and Looking Glass. The military would have been wiped out. Food production would be largely unaffected for grains and vegetables, but nearly every nonhuman animal in the midwest, coastal cities, and big sky parts of the country would be dead from fallout. Food delivery and distribution would rely largely on coal rail and river barge transport, but it still did mostly at the time. It would take ten years to rebuild a refining capacity and restore the power grid and military Things would eventually return to normal. The cities would be rebuilt and reinhabited.
I know it is hard to believe, but look at Hiroshima, Nagasaki, German firebombed cities from WW2 like Dresden; they were rebuilt from the ashes. Germany was nearly entirely destroyed by WW2. It came back.
Barring nuclear winter actually occurring (which the Kuwait oil field fires kinda proves won't happen), total nuclear war is something countries can recover from, which makes it even more likely to happen in the future. As Ellsberg put it, "any nonzero chance is crazy."
https://apjjf.org/-Daniel-Ellsberg/3222/article.html
The exact quote that stunned me being:
"The total death toll as calculated by the Joint Chiefs, from a U.S. first strike aimed primarily at the Soviet Union and China, would be roughly 600 million dead. A hundred Holocausts.
I remember what I thought when I held the single sheet with the graph on it. I thought, this piece of paper should not exist. It should never have existed. Not in America. Not anywhere, ever. It depicted evil beyond any human project that had ever existed. There should be nothing on Earth, nothing real, that it referred to."
Imagine reading memos with stuff like "we plan to kill at least 600 million people, probably a lot more, a lot of them our allies"....