No. Default is when the bond issuer doesn't pay interest.

The US government can let the bonds default by not paying. This can be by not issuing new debt (or getting the fed to print more money).

That harms USD Value not so much government operations, so in a roundabout way it actually makes the US Debt slightly less from a pure value perspective. The USA system is such: Government Deficit equates to Loans taken out from US Banks, meaning $38.876 Trillion USD is owed from USA Federal Government to the US Banks.

Meanwhile, more about bonds, between $2.3 and $3 Trillion USD worth of bonds gets issued inside and outside the USA every year for the past 30 years (bonds fulfill in either 15 to 30 years) so if every nation on earth (and their citizens) and the US Citizens suddenly traded in their bonds all at once then it could cause a lot of headaches for the US state but at the end of the day as long as US Banks are willing to loan them cash then it has infinite money.