It's not sustainable, but politicians are betting they can kick the can down the road long enough to get theirs.
Hatari is right, there isn't enough of the budget that's touchable to make a difference even if you cut it to zero. Entitlements are such a massive part of the budget that they're impossible to rein in. The majority of government spending is entitlements and there's a bunch more that are hidden behind cute names like "earned income tax credit" so they don't have to call them welfare, though that's exactly what it is. You could completely eliminate defense and still not come close to knocking down the national debt.
I don't know when it's going to come crashing down, hopefully not in my lifetime, but it will eventually.
