We're living on borrowed time because we're living on borrowed dime. As deficit spending increases, the share of the Federal budget that goes to servicing the debt (currently about 8%) increases, crowding out other spending. If we keep racking up more debt, the amount we spend on servicing the debt will eventually eclipse the entire Federal budget, then the entire GDP of the US, and by about 2092, it will eclipse the GDP of the entire world.
Let me repeat that: if we continue spending the way we have been, then before the end of the century, we will have to spend more to service our debt than the gross domestic product of all nations on Earth combined. Which, obviously, is impossible. Which only leaves two options: defaulting on loans or printing money Zimbabwe style, which will destroy the purchasing power of the US dollar and leave everyone in the US earning those US dollars unable to buy anything with them. You'll need a billion dollars to buy a loaf of bread. And most of us don't have that much.