In the minds of Trumpsters, If you don't like the President, then you need to be fired.
It's an impressively dumb argument, basically that if you personally dislike someone you can't professionally investigate them.
That means when law enforcement is investigating mob bosses, serial killers, child rapists, etc, they can only investigate them with agents who feel neutral or positively disposed towards child rapists and serial killers. What sort of psychos would you need to hire to fulfill Spidey's ideas on who is allowed to investigate people?
