AIPAC is a powerful player in DC. Someone, almost certainly them, leaked they are privately furious about Bannon appointment. Many on Twitter are urging them to go strongly public about it.
Jeet Heer has some thoughts about this, and how this is an opening, an opportunity for anti-Trump forces (which include many Republicans,) to splinter the already shaky Trump coalition. Look, Trump had to appoint Bannon and Priebus together because neither could defeat the other. This indicates a coalition ripe for disruption.