Credit ratings of countries that control their own central bank and only issue bonds in their own currency are kind of just make-believe. They only matter as much as people play along…
Although the debt limit thing is a risk, there’s no practical or financial reason why the US would ever default on its bond payments, but the debt limit brinkmanship creates a potential to default due to politics (for no real reason).
They're not make-believe. Plenty of insurance companies and pension funds can only invest in AAA-rated investments. Will their policies change to accommodate downgrades? Possibly. But there's a very real risk of lessened demand for treasuries.
Although the debt limit thing is a risk, there’s no practical or financial reason why the US would ever default on its bond payments, but the debt limit brinkmanship creates a potential to default due to politics (for no real reason).