But if other countries tried to maintain the levels of US deficit / debt, they were given far less lenience from investors, in pressure / yields. This was because US was seen as, on the whole, fiscally responsible, very productive, and safer from shocks - to the point that when the US mortgage crisis exploded, the safe haven for assets was… the US.
As these assumptions are challenged, the US is waking up to what the European old economies experienced following 2008. Increasingly yields, increasing costs of borrowing etc.
If you’re reliably printing good GDP growth, higher level of debt may be good as it gives you more leverage, and drives more growth in turn. But leverage is a multiplier and it isn’t free, so if the engine sputters, you might find yourself falling out of the car at a greater speed…