"At the pleasure of the President" talking point == Authoritarianism
What this Republican talking point--shamefully repeated by Pravda on the Potomac--really means is that the will of the President trumps the rule of law.
Nobody is claiming that the President doesn't have the right to hire and fire the USAs--unless that would break the law. (And it's certainly not usual for only some to be fired, not at the start of a Presidential term. And if the firings were so very, very OK, then why has the Justice Department had such a hard time coming up with a reason for doing it? Oh, not the incompetence dodge again!)
If firing the USAs would be a case of obstruction of justice or abuse of power--and the 8 were fired either because they were investigating Republicans or they refused to gin up charges against Democrats--then the President doesn't get to fire them, whether that would give Him pleasure or not, because that would be illegal.
This virulent "pleasure of the President" meme is Nixon's when the President does it, that means it is not illegal" all over again, except this time the Beltway 500 agrees with Nixon.
This virulent meme is authoritarianism in its purest form, entirely lethal to Constitutional government and the rule of law.
The Beltway culture really is a fascist cesspool.