U.S. President Donald Trump's relationship with Elon Musk soured quickly this week, as the billionaires feuded publicly.

ALEX BRANDON/THE ASSOCIATED PRESS

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It took less than five months, but Elon Musk has repealed a more-than-half-century-old political science principle established by the singer Neil Sedaka. Mr. Musk has shown that “breaking up is hard to do” – the title of the crooner’s most famous song – doesn’t apply in Donald Trump’s Washington.

Actually, in the case of Mr. Musk and his patron Mr. Trump – the power balance between the two billionaires was never quite clear – breaking up wasn’t that hard at all.