“These conferences are supposed to be cohesive unity builders,” Mr. Miller said. But, he added, “rarely has Israeli politics been more divided, and Aipac is going to mirror those divisions.”

Republicans will almost certainly use the conference to portray their party as the home for Israel’s supporters. Senator Mitch McConnell, Republican of Kentucky and the majority leader, is expected to talk about legislative efforts to support Israel and to oppose anti-Semitism. Representative Kevin McCarthy, the House Republican leader, will tell conferees that “Aipac should not be boycotted. Aipac should be celebrated,” said his spokesman, Matt Sparks.

For Democrats — who for decades have relied on the Jewish vote — the task will be trickier. They must reiterate their support for the Jewish state without alienating progressives, including millennials and many young Jews who are increasingly willing to accuse Israel of human rights abuses.

“It will be interesting to see if Democratic leaders who are going to be speaking at Aipac are going to be speaking about Israeli policy as well, where they see differences with them,” said Yousef Munayyer, the executive director of the U.S. Campaign for Palestinian Rights. “The applause lines that are going to go over well with Aipac are not going to go over well with the rest of the Democratic Party. That tension will really be on display here.”

Mr. Hoyer, the Democratic leader, will speak on Sunday evening. He plans to remind his audience that the Jewish state and the United States-Israel relationship have “broad, bipartisan support because most Americans see them as integral to standing up for America’s values and our national security and interests,” according to a spokeswoman, Annaliese Davis. He will also “talk about what Israel and America have in common as fellow democracies,” and the threat posed by Iran.

Washington, meanwhile, has been gearing up.

Mr. Trump announced on Thursday that the United States should recognize Israel’s authority over the Golan Heights, a reversal of longstanding policy against accepting territorial changes acquired by force. The strategic area was seized from Syria in the Six-Day War of 1967. The policy-by-tweet was a valuable election-eve gift to Mr. Netanyahu.