You have a friend named Old Wang, who spends money lavishly, spending more each year than he earns. If a normal person did this, the bank would have stopped lending him money long ago, or would charge very high interest.

But Old Wang is different. His father runs a printing press.
Every time Old Wang issues bonds to borrow money, if no one on the market buys them, his father pays to take them. Because he has a printing press dad providing unlimited backing, the interest on Old Wang's borrowing has always been very low — after all, creditors know "his dad will take over."
So Old Wang acts without restraint, borrowing more and more, the hole growing larger, not caring even if the deficit reaches 5.8% of income. After all, with his dad around, borrowing is no worry.
Now Warsh's point is: it's time for his dad to stop.
If his dad no longer buys, Old Wang will have to borrow on the market at prices based on real credit. The market takes a look — goodness, your annual hole is that big? Interest doubles.
Old Wang is forced to face real consequences: either spend less, or earn more.