Minnesota Rep. Betty McCollum's comments mark the first time a Congress member has referred to the lobby as such.
“These members of Congress are really trying to send a message that everything’s fine. But I don’t think the crowd believes it, and I don’t think they believe it.”
Seven Democratic presidential candidates so far have confirmed they won't attend.
The resolution decries anti-Semitism, in addition to anti-Muslim discrimination and white supremacy, but it doesn’t mention Omar by name.
The backtracking over the appointment comes ahead of the crucial New York state primary. Sanders has been campaigning heavily in New York City, where nearly 20 percent of Democratic primary voters tend to be Jewish.
A young Jewish activist with a history of criticizing Israel has just been named Bernie Sanders' National Jewish Outreach Coordinator.
The president of AIPAC said she was disappointed that attendees applauded as Trump went off-script to call Obama "the worst thing to happen to Israel."
Trump was warmly received, delivering an unusually scripted speech from a teleprompter before the nation's largest gathering of pro-Israel activists.
Clinton went after Trump for repeatedly saying he would be "neutral" on Israel and for his campaign's rhetorical attacks on immigrants, Mexicans, and Muslims, saying "America should be better than this."
In a major foreign policy address on Wednesday, the president said the choice is between the deal or war.
Recent polls suggest Americans are at odds over the agreement — even though most people aren't familiar with the details of the highly technical accord.