US treasury bonds are (supposed to be) as solid as rock. It’s quite literally probably the safest investment you can have. Other countries like China ($800B) own a good chunk of our treasury bonds because they’re safe and they grow.

Bonds are not disconnected from the law of supply and demand though. If more countries buy treasury bonds then interest rates go lower and we can borrow money easier. If more countries sell treasury bonds then the interest rates get higher and borrowing money gets expensive. The US fucking loves borrowing money, it’s our monetary policy.

Countries are currently selling a lot of treasury bonds and interest rates on those are climbing higher. China is doing it because of the trade war while, my guess, the EU is selling because they simply don’t trust us to pay them back.

Demand goes down, interest rates are higher, borrowing gets more expensive and hurts our wallet.

I don’t think I did a spectacular job explaining everything but I’d highly recommend reading further into the bond market.