JERUSALEM (NYTIMES) - It started, as it has in US presidential races for decades, as a campaign line, one that weary Israelis and Palestinians hear but rarely take seriously: Mr Donald Trump promised to move his nation's embassy to Jerusalem from Tel Aviv.

But by Thursday (Jan 19), the eve of Mr Trump's inauguration, those decades of promises seemed very real - with reverberations far beyond stone and cement.

Mr Trump himself made perhaps his strongest statement on the issue on Thursday, telling a conservative Israeli news outlet, "You know I'm not a person who breaks promises."

Palestinians protested around the West Bank on Thursday, and many Israeli Jews wondered if this was a gift that could be politely pushed away. Moving the embassy is not even close to the top of the list of concerns for even right-leaning Israelis who oppose the establishment of a Palestinian state.

Many worry it would only set off new fighting with the Palestinians as well as the rest of the Arab world, a big price tag for a symbolic change that would hardly move the ball on the broader conflict.

"I don't know what's in it for Trump," said Mr Akiva Eldar, a longtime Israeli columnist and co-author of a book on the issue of moving the embassy. Mr Eldar's thesis was that this was largely a concern for US politicians, not Israelis or Palestinians - and even within the United States, it was not generally advocated by those with experience on the ground.

"If you talk to serious people, if you ask the secret service, they say don't do it," Mr Eldar noted. "They don't think it's worth it. Everything is so fragile right now."

Amid the West Bank protests on Thursday, Mr Saeb Erekat, the chief Palestinian negotiator, said moving the embassy would be a "red line" that, if crossed, could kill a two-state solution, reduce US influence in the peace process, and possibly set off a new round of violence.

"Why would a president-elect decide to begin his presidency by playing with the blood of Palestinians and Israelis?" Mr Erekat asked in an interview. "Why? For whose sake?"

He said that if Mr Trump were to follow through, the Palestine Liberation Organisation would repeal its recognition of Israel, considered a baseline condition for peace talks. "I hope he does not do it," Mr Erekat added.

Jerusalem is the seat of Israel's government, but it is not home to any foreign embassies. US policy, like that of many other nations, has long been that the future of the holy city can be determined only as part of a broader peace agreement and that putting the embassy there would prejudge the outcome.

The Israeli leadership considers Jerusalem, including territory captured from Jordan in the 1967 war, its united and eternal capital. But Palestinians see Jerusalem as the capital of their future state.

If Mr Trump does in some way move the embassy to Jerusalem - and there are various situations, including having his ambassador simply set up shop in the existing US Consulate - it would be seen as a victory for Israel's right wing, which has been gaining political dominance over many years (and power in Washington: The leaders of two Israeli settlements, condemned by past administrations, are attending Trump's inauguration).

It would also be considered a rebuke to the Obama administration's refusal last month to veto a UN resolution condemning settlement building in the occupied West Bank as it warned of the slow strangling of a two-state peace.

"It is hard for me to imagine any Israeli on the right or even on the left who thinks Jerusalem is not the capital of Israel and would not welcome in their heart recognition of that by the US," said Mr Moshe Arens, a former defence and foreign minister from the Likud, the governing party led by Prime Minister Benjamin Netanyahu.

But even some on the right have questioned the move's value and timing. In December, Mr Avigdor Lieberman, the hardline defence minister, appeared to say it was not a priority.

"We saw in all the American election campaigns that they say they will move the embassy to Jerusalem," Mr Lieberman said at a forum in Washington. "We have enough challenges around us, and I think it would be a mistake to turn the matter of the embassy into a central one."

Privately, other conservatives have questioned whether the symbolic value of an embassy move is worth the risks in terms of a potential Palestinian uprising and deterioration in Israel's relationship with other Arab neighbours like Egypt and Jordan. But as Mr Trump's promise seems more inevitable, some have publicly cheered it.

"We welcome it," Mr Danny Danon, the Israeli ambassador to the United Nations - who opposes a Palestinian state - said in an interview on Thursday. "Jerusalem was the capital of the Jewish people 3,000 years ago."

There is as much discussion of whether a new Trump administration would move the embassy as exactly how, and some believe that could either soften the blow or make it harder for Palestinians and Arab states to accept the change quietly.

The US Embassy, and its hundreds of employees, are in Tel Aviv, as are those of nearly all other countries. The US Consulate General's home and office, which handles relations with Palestinians, is in West Jerusalem, and a US consular office is close to the line that divides East and West Jerusalem and provides visas and similar services.

Experts agree that neither of these locations could house a modern, secure US embassy immediately. So a range of options are being discussed.

One could be as simple as changing the sign on the consulate in West Jerusalem, which processes the visas for Israelis, as the State Department looked for and built a more permanent embassy - something that would take years. In another, Mr Trump's nominee as ambassador, Mr David Friedman, who is aligned with the Israeli far right, supports the settlements and has a residence in Jerusalem, would work out of the West Jerusalem consulate - without an immediate declaration of it as the embassy.

Neither of those options is acceptable to the Palestinians, Mr Erekat said. The symbolism remains too strong, favouring Israeli claims against those of Palestinians. The question of capitals, he said, is not for other nations to decide, but something to be negotiated between the two principals.

"This will destroy us as Palestinian moderates," he said. "This will bring extremism to the region."