Yet of all the issues that have defied resolution despite decades of talks between Palestinians and Israelis, the final status of Jerusalem — with its sites holy to Jews, Christians and Muslims, and warring claims dating back to the Crusades and the Romans — has been uniquely nettlesome.
The United States has taken pains to refrain from recognizing the Holy City as Israel’s capital precisely to avoid being seen as prejudging the outcome of peace talks, in which Palestinians seek to make East Jerusalem the seat of their eventual government.
Hanan Ashrawi, a member of the Palestine Liberation Organization’s executive committee, said dispensing with that longstanding reticence would reveal the United States as “so incredibly one-sided and biased” that it “would be the total annihilation of any chances of peace, or any American role in peacemaking.”
“They’re sending a clear message to the world: We’re done,” she said.
While physically moving the embassy would require little more than putting a new sign on existing American consular offices in Jerusalem, Mr. Trump’s declaring Jerusalem the capital would carry great symbolic power, Palestinian officials said.
“If anything, it is worse, actually,” said Nasser al-Kidwa, a member of the central committee of Fatah, the dominant P.L.O. faction, and a nephew of Yasir Arafat, its onetime leader. Recognition matters, he said, “not the stones” of an embassy building.
Ahmed Yousef, an adviser to Ismail Haniya, leader of the Palestinian militant group Hamas, was similarly critical of Mr. Trump’s expected declaration. “I don’t understand why he wants to antagonize over a billion Muslims around the world,” he said.
The specific way in which Mr. Trump makes his declaration, however, could mean a dramatically different response on both sides of the conflict.
If he just refers to “Jerusalem” as Israel’s capital, or refers to the city’s present municipal borders, Mr. Trump would be likely to set off a strong backlash in much of the Arab world, analysts said.
“For Palestinians, this will be perceived as dividing the cake while negotiating over it,” said Ofer Zalzberg, a Jerusalem-based analyst at International Crisis Group.
Ms. Ashrawi warned it could lead to repercussions “that would not be easily contained,” including violence: “To people who are looking for an excuse, this would be a ready-made excuse.”
If Mr. Trump were to limit his statement to West Jerusalem, however, it would likely antagonize supporters in the pro-Israel camp, by undercutting their claim to a united capital throughout the city and acknowledging Palestinian designs on East Jerusalem.
Any attempt at deliberate ambiguity is unlikely to fly because the United States will be forced to specify the territorial definition of Jerusalem that the president was relying upon, said Daniel Shapiro, who was President Barack Obama’s ambassador to Israel.
“It accomplishes so little that I wonder if it’s worth that headache,” he said.
The timing of Mr. Trump’s declaration was baffling both to those who warned against it and some who welcomed it.
Both sides of the Israeli-Palestinian conflict are awaiting a proposal by Mr. Trump’s administration to restart the peace process. And recent meetings in Riyadh between Saudi Arabia’s crown prince, Mohammad bin Salman, and, in turn, Mr. Trump’s son-in-law, Jared Kushner, and the Palestinian president, Mahmoud Abbas, have fueled speculation that Mr. Trump and Prince Salman are trying to push through a plan.
Given the prince’s eagerness to combat Iran, Palestinians are concerned he could embrace a proposal unfavorable to them, for an alliance with Israel against Iran.
But Arab governments, even Saudi Arabia’s, could be compelled to rebuke a declaration of Jerusalem as Israel’s capital, experts said.
“Pushing this issue now, in advance of a peace process at a time when the administration has zero credibility on this issue, at a time when it wants to engage the Saudis, makes absolutely no sense,” said Aaron David Miller, a former Mideast peace negotiator under past Republican and Democratic administrations. “It’s a self-inflicted wound.”
Perhaps no Arab leader has more at risk in a cementing of Israel’s hold on Jerusalem as its capital than King Abdullah II of Jordan, whose dynasty has defined itself as the custodian of Al Aqsa, Islam’s third-holiest site, which is in Jerusalem.
While the king can fire subordinates who fail him, he is viewed as personally responsible for Al Aqsa, said Mr. Zalzberg, and Mr. Trump’s declaration “could contribute dramatically to the erosion of the king’s popularity and legitimacy.”
Abdullah has been in Washington for more than a week, pressing the administration not to take this step, according to Arab news media. Petra, the Jordanian news agency, said the king had warned that changing the United States’ posture on Jerusalem would threaten a two-state solution and “could be potentially exploited by terrorists to stoke anger, frustration and desperation in order to spread their ideologies.”
Palestinian officials across the political spectrum made similar warnings. In Gaza, Hamas issued a statement calling on Palestinians to “incite an uprising in Jerusalem so that this conspiracy does not pass.” Mr. Yousef, the adviser to the Hamas leader, said Mr. Trump’s move would drive up anti-American sentiment and “decimate whatever good will they have here.”
And a Hamas representative based in Lebanon, Ali Barakeh, said the group would probably respond to Mr. Trump by calling for a new intifada, or uprising, and for Mr. Abbas to quit negotiations, “since the Americans won’t achieve anything for them.”
But Ayman Rigib, a Fatah leader in Cairo, worried that Mr. Abbas would not push back firmly enough. “This is a new low for us as Palestinians,” he said. “We are not only weak, we also have a leader who might actually accept this deal.”
Along the 1967 line in a Jerusalem quieted by the Jewish Sabbath, Hani Juwaihan, 28, one of the relatively few East Jerusalem Palestinians with Israeli citizenship, said he wished Mr. Trump would leave well enough alone.
“It’s not his right to decide,” said Mr. Juwaihan, who lives in the Al Thuri neighborhood of East Jerusalem but works as a cook at La-La Land, a restaurant near the beach in Tel Aviv.
“If there’s peace, all well and good, we’ll live together without any problem,” he said. “But in the absence of peace, it’s not for Trump to decide. Jerusalem is a holy place. Nobody can decide.”