What is, and isn't, worrying about 100% debt to GDP

The US national debt has surpassed its gross domestic product, with a debt-to-GDP ratio of over 100%, and is projected to continue rising to 120% by 2036. The Congressional Budget Office projects federal revenue will be 17-18% of GDP, while expenditures will be over 23% of GDP. This gap is expected to lead to an ever-rising debt-to-GDP ratio.