WASHINGTON — Some are standing with President Obama. Some are protesting the actions of the House speaker, John A. Boehner. Still others say they do not want to be props in Prime Minister Benjamin Netanyahu’s re-election campaign.

By Monday afternoon, 49 House and Senate Democrats had announced they would not attend the Israeli prime minister’s speech to a joint meeting of Congress scheduled for Tuesday, according to a running tally in The Hill. That total represents an unprecedented rebellion that is all the more striking because allegiance to Israel has long had nearly unanimous support in Congress.

“It is improper for the speaker of House to side with a foreign leader who is coming in to rebut the chief executive and commander in chief of our country as he is trying to negotiate a peace deal to stop Iran from acquiring a nuclear weapon,” Representative Keith Ellison, Democrat of Minnesota and one of two Muslims in Congress, told a Minneapolis television station this past weekend. “I think we should stand with the commander in chief.”