The moment had finally come, and it was every bit as lowdown, vindictive, personal, petty, operatic, childish, consequential, messy and public as many had always expected it would be.

“One thing’s for sure,” Elon Musk posted on X midway through his relentless hourslong attack on Donald Trump, “it ain’t boring!”

The clash of the titans was upon us, and the gloves were off.

The speed of the fallout was breathtaking. Up until about 14 seconds ago, Mr. Musk was flying on Mr. Trump’s planes, staying at his homes, socializing with his children. On Friday, Mr. Trump celebrated him with an Oval Office farewell address and gave him a novelty, oversize key to the White House.

But all was not well. Mr. Musk had been stewing about the sweeping domestic policy bill that the White House was pushing through Congress. By Thursday afternoon, he started spitting venom.

“Without me, Trump would have lost the election,” Mr. Musk wrote on X. “Such ingratitude.”

How sharper than a serpent’s tooth it is!