Because there are no replacements, no one who would accept a position in the Trump administration.
Seems Kelly hates his job but realizes how unhinged Trump is and stays.
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According to Vanity Fair:
‘Two senior Republican officials said Chief of Staff
John Kelly is miserable in his job and is remaining out of a sense of duty to keep Trump from making some sort of disastrous decision. Today, speculation about Kelly’s future increased after Politico
reported that Kelly’s deputy
Kirstjen Nielsen is likely to be named Homeland Security Secretary—the theory among some Republicans is that Kelly wanted to give her a soft landing before his departure.
‘One former official even speculated that Kelly and Secretary of Defense
James Mattishave discussed what they would do in the event Trump ordered a nuclear first strike. “Would they tackle him?” the person said. Even Trump’s most loyal backers are sowing public doubts. This morning,
The Washington Post quoted longtime Trump friend
Tom Barrack saying he has been “shocked” and “stunned” by Trump’s behavior.’