Conservative organizations are targeting Republican senators, saying that they will pay a price if they do not back the president-elect’s choice for defense secretary.

The comments highlighted rifts within the U.S. right wing and between two men who have been influential advisers to President-elect Donald J. Trump.

Mr. Musk has fallen out with prominent right-wing Americans who say they are worried that their agenda may be sidelined in favor of his own — and that he is willing to silence them on X.