National debt isn't like personal debt.
The more debt your economy can sustain the more powerful it is and that's why United States has the most powerful economy in the world, they can keep spending but not tipping over.
This is also why China is on the rise atm, they are spending like it's no ones business, investing in their own country and other countries around the world, but they can sustain their national debt.
You have to remember a country is more than just a country it's also a business, some leaders run their business very well and some don't.
Give an example as well here let's say you have a credit card, every month you are paying the minimum (which is interest), your debt isn't going down but your building your credit, your line of credit is becoming more powerful even though your debt is remaining the same since you are only paying off the interest on your debt.