The US by definition can't default on its own debt. It's literally impossible because all debt is in USD. If the US gets into the situation where it doesn't have enough money to pay off its interest payments, the only one solution is to print more money to pay off the debt. This will lead to #2 in your list, which is actually just #1.
When the US starts printing money, it will lead to a lot of destruction of assets because China will also start selling their UST causing interest rates to jump. I can see a weird situation where inflation starts to jump but also interest rates jumping as well.
It can default on its debt by .. refusing to pay it. Remember all the debt ceiling fiasco and the furlough of federal workers? It would be a huge moment of voluntary stupidity, but anything's possible.
If you have the ability to pay your debt by printing more money, but then default because you don't, is absurd. It just won't happen. They would never choose to not pay when they can simply print more money.
If you want to go down that route, you can say that the US can also cancel its own debt by threatening every country that owns its debt with nuclear missile attacks if they don't cancel the debt.
And a big chunk of the 'funds to run' go to servicing existing debt. This is a big part of why interest rates never substantially increased to pre-GFC levels. Governments would never be able to afford the higher interest rates.
When the US starts printing money, it will lead to a lot of destruction of assets because China will also start selling their UST causing interest rates to jump. I can see a weird situation where inflation starts to jump but also interest rates jumping as well.