“The ash plume from a large explosion at Yellowstone would screw up agriculture half way across the United States...the world’s bread basket.”
Only temporarily.. like a 1000 years or so. Remember the Yellowstone caldera helped create our bread basket. After the ash has landed and nature and weather work on it it is terrific farming soil.
But only like a 200 or more generations after the event.
For those living when the event occurs, it will be a major league catastrophe. Perhaps another near extinction event like the Toba eruption.