Progressives in the House and their allies have rallied to the defense of Ms. Omar, a freshman Democrat from Minnesota and one of the first two Muslim women elected to Congress, who was hailed as a trailblazer. Speaker Nancy Pelosi told top Democrats on Tuesday evening that the resolution would also include language condemning anti-Muslim bias as well — a move advocated by the Congressional Progressive Caucus.
The rift emerging around Ms. Omar is easily the most serious since Democrats swept to House control in November, an ideological and generational divide that has grown fierce in recent days and threatens to overshadow the party’s legislative agenda.
On one side are veteran Democrats like Representatives Eliot L. Engel, Nita M. Lowey and Jerrold Nadler — all of whom lead major House committees and all of whom are Jewish. They spoke over the weekend, and some had talks with Representative Steny H. Hoyer, the majority leader, in a frenzied effort to respond to Ms. Omar. They emerged to push for the resolution.
On the other side are younger members like Representative Alexandria Ocasio-Cortez, Democrat of New York, and liberal groups like Justice Democrats and IfNotNow, a movement of young Jews dedicated to ending the Israeli occupation of the West Bank. They accuse Democratic leaders of singling out a woman of color while letting slide comments from Republicans that they deem racist, anti-Semitic or bigoted, including many from President Trump.
“One of the things that is hurtful about the extent to which reprimand is sought of Ilhan is that no one seeks this level of reprimand when members make statements about Latinx + other communities,” Ms. Ocasio-Cortez wrote on Twitter, mentioning a Republican House member who shouted, “Go back to Puerto Rico” on the House floor.