what did jamie dimon say about the bond market?

I have been hearing people talk about Jamie Dimon saying there will be some kind of crack in the bond market but i can't really wrap my head around the whole thing. Can anyone explain please?

He said something about US bonds no longer being AAA rated but that they have been downgraded to AA. He also said borrowing during covid 19 has put an enormous interest rate burden on US so the bond market is overburdened