Ms. Ocasio-Cortez, a liberal firebrand from the Bronx, has given her chief of staff, Saikat Chakrabarti, remarkable latitude to pursue the divisive politics that made his name when he led Justice Democrats, a group founded to challenge entrenched Democrats through primary campaigns.

With that license, Mr. Chakrabarti has become an unelected symbol of the party’s growing disunity, as Democrats try to coalesce as a party before what promises to be a punishing fight next year for the White House. The battle between the Democrats who secured the House majority last year by flipping Republican districts and the smaller, but politically potent, left-wing from secure Democratic districts has found its cause célèbre…

The drama may be more reminiscent of a high school student council than the House of Representatives, but it has created a dilemma for Ms. Ocasio-Cortez. The progressive darling has remained silent on her aide’s remarks; her spokesman declined to comment on Saturday. Asked on Thursday to comment on her aide’s earlier tweets, Ms. Ocasio-Cortez replied that she had “not been paying attention to this.”

That is likely to further anger House members, many of whom are people of color representing moderate to conservative districts. It is considered a breach of protocol for unelected congressional aides to criticize lawmakers even in closed-door meetings — much less publicly blast out their grievances — and those who step out of line typically face consequences.