Potatoes, a new world food, were a monoculture in Ireland at the time. These days there are a huge number of potato varieties grown, so a devastating potato blight seems unlikely to occur again.
How devastating? I expect few if any would starve; we grow more than enough grain to keep people alive. Potatoes farmers would be put in a hard financial situation, but they'd probably get bailed out and could replant with other varieties for the next season.
I don't think the bar is as low as "could the government make enough gruel to keep you from starving." And, given the current experience with vaccine distribution, even that is not certain.
Think of all commercial food products that contain potatoes that could no longer be produced for a time. Potatoes are a significant source of cattle feed. Potato starch has many non-food industrial applications.
Perhaps we wouldn't have millions of deaths, but a year without potatoes would be an historic catastrophe that Americans would remember for decades.
