Sean Spicer, during an interview with the BBC, regretted his poor performance in discussing the size of the Trump inauguration crowd on his first day as Press Secretary. he then uttered this classic. It is a mashup of “set the tone” (establish the manner in which something will be conducted) and “the die is cast” (a course of action is finalized). My guess is that the speaker was thinking of die casting, the process used to produce metal parts. Given the amount of lies from Mr. Spicer’s boss’s lips in the past two years, I think he definitely set the die.
“My Ol’ Pal” has a slightly different take. She says: “When Julius Caesar crossed the Rubicon, he was said to have stated “The die is cast,” meaning that he had decided the fate of Rome. Perhaps Sean Spicer was thinking that he had determined the future of the administration’s falsifications with his pronouncement about the size of the crowd at the inauguration.” Indeed. For the quote, see 3:55 mark at: https://www.bbc.co.uk/programmes/p06fkvhp