> US could simply sign a favorable (for Iran) deal while waving a white flag emblazoned with "Mission Successful

Trump is constitutionally[1] unable to do that. He cant compromise or look weak, or it'll conjure the ghost of Fred Trump calling him a loser one more time. Ironically, this fear of losing is how becomes a loser: first against(!) Covid-19, when he thought wearing a mask made him look weak, and now against Iran.

1. His make up, not the document