I think the seriousness of this would be such that even a Democrat president would have to respond.
Regretfully, I disagree. It is the nature of the Democrat to appease. There would be a diplomatic threat, but no punitive military action.
Or in other words: If Israel was struck by three nuclear weapons from Iran, what would (A) Jimmy Carter, (B) Bill Clinton, (C) John Kerry do?
Scary, huh?