If you are worried about your grandchildren having to pay the current debt, worry instead about them finding jobs in the age of robotics. That will be their real challenge.
Alexander Hamilton argued successfully for a national debt because then other countries will have a stake in America.
Here Krugman points out that government debt is money borrowed from itself. If I take money from my purse and put it into a checking or saving account, I am not in debt.
Students, whatever your major or interests, it is important to understand the debt; it will make you a better voter and a better citizen. Let Paul Krugman explain it.