When Israel's routine hostility toward Gaza once again flared into full-on battle last month, Nancy Pelosi, the Democratic party leader in the US Congress, sent out a tweet:

That was pretty much the sentiment of just about everyone in the US political establishment, from the president to the unanimous support in both houses of Congress for a resolution giving unconditional backing for Israel's bombing of Gaza.

So, it was with the solid opposition to the Palestinian request for recognition of a state at the United Nations. Susan Rice, the US ambassador to the UN, may have looked isolated in casting the only vote by a major power against Palestinian statehood, but Washington's political establishment was fully behind her.

On one issue, however, America's vehemently pro-Israel politicians are much more muted – and it may reveal to Palestinians a chink in Israel's armour in the US. The prime minister, Binyamin Netanyahu, decided to punish the Palestinians for the UN vote by announcing the expansion of existing Jewish settlements and advancing a plan, known as E1, to link Jerusalem with one of the biggest Israeli colonies in the West Bank, Maale Adumim. That would eat significantly into any Palestinian state and, more importantly, further seal off occupied East Jerusalem from the rest of the West Bank, as part of the long term Israeli strategy to claim the entire city.

Netanyahu argued that the Palestinians going to the UN was a threat to peace. Almost everyone else regarded the settlement announcement as a far bigger blow to an agreement to end the conflict.

The White House finally spoke up: Barack Obama criticised the E1 plan as "especially damaging". Congress did not rush to condemn him. Even the pro-Israel lobby, led by the American Israel Public Affairs Committee (Aipac) did not thrust itself to the forefront of defending Israel. And Hillary Clinton, the US secretary of state, last year called the settlements "illegitimate".

Now, the Palestinians are floating the prospect of going to theInternational Criminal Court (ICC) over the settlements. It would be a smart move – if they can resist the inevitable pressure from the west not to do it.

In all the wrangling over recognition of a Palestinian state at the UN, there was much hand-wringing in western capitals over the Palestinians gaining access to the ICC. And the Israelis are more fearful of the court than they let on publicly.

The US and the British tried to get the Palestinians to renounce the right to accede to the ICC, on the grounds it would complicate a nonexistent peace process. However, it is hard to imagine that Washington and London were not also worried about the implications if the court moved on from accusing African despots and warlords to charging soldiers and officials of a close ally, armed by the west, with war crimes in Gaza.

But now, the Palestinians have raised the prospect of a different ICC action, over the settlements, following the E1 announcement. The Palestinian foreign minister, Riad Malki, said this week that if Israel pushes ahead with the settlement construction, his government will look to the court for redress.

"Then we would be able to prosecute Israel for all the war crimes it perpetrated against our people in the past, especially the construction of settlements," he told Voice of Palestine radio. "It all depends on whether Israel would continue with its settlement plan."

Palestinian President Mahmoud Abbas said much the same during a visit to Turkey. Israel's colonies in the West Bank are a clear breach ofinternational law under Article 49 of the 1949 Geneva Conventions, which bans on an occupying power from moving its civilian population onto occupied territory – a clause included, in large part, because of Nazi attempts to colonise areas of occupied Poland by planting Germans there.

Israel's defence is that the West Bank is not strictly occupied territory because it does not belong to another state. But the UN vote has arguably changed that. Israel has also tried to say the settlements fall under the conventions' allowance of construction as a military necessity. But it's hard to make a case for defence when the Israeli government's policy is to funnel Jewish immigrant families into the settlements and to give tax breaks to encourage people to move to them.

In any case, the United Nations security council, the International Committee of the Red Cross, the International Court of Justice and the High Contracting Parties to the Geneva Conventions all say the Israeli colonies are a breach of Article 49. No government other than Israel, not even the US, regards the settlements as legal.

The Israelis are nervous about legal action. They call it "lawfare". It is potentially effective because taking on the Jewish settlements does not threaten Israel's right to exist. It is not violent. It is not terrorism. And there's not many governments going to rush to Israel's defence.

A legal fight at the ICC would lay bare the annexation and dispossession behind Israel's settlement strategy – the theft of land from Palestinians, the practice which sees Jewish colonies enjoy unlimited cheap water, while nearby Arab villages are subject to rationing and higher charges, the policy that says a Jewish immigrant from Russia has a greater claim to the land than a Palestinian born on it. And that's without even getting into the broader scheme to claim as much territory as possible for Israel and leave a rump Palestinian state.

Israel's settlement policy has been to act piecemeal and count on the rest of the world not having the stamina for a fight – successfully, as it turns out. What it does not want to have to do is defend the settlements in their entirety before an international court, with the risk of being ruled a rogue state in breach of the laws of war.

There's also a domestic concern. An ICC case might even prompt a more robust debate in Israel where opinion polls show there is no great support for the settlements. If the ICC were to declare the settlements illegal, it would raise other interesting possibilities for Palestinian legal action. Would foreign banks still be prepared to transfer the millions of dollars donated by Americans to settlement construction, or to buy property in the occupied territories, if they knew it was a breach of international law?

Europe is already moving in that direction. European Union foreign ministers said this week that agreements with Israel do not apply to Jewish settlements in the occupied territories – a move Israel fears is laying the groundwork for economic measures, such as the labelling of exports originating in the colonies. The EU said all of its agreements with Israel "must unequivocally and explicitly indicate their inapplicability to the territories occupied by Israel in 1967 – namely, the Golan Heights; the West Bank, including east Jerusalem; and the Gaza Strip."

The EU is also talking about banning violent settlers, responsible for a string of attacks on Palestinians, who are not prosecuted by the Israeli authorities, from within its borders.

An ICC ruling in favour of the Palestinians might have another effect. When Obama first came to power four years ago, he attempted to strong-arm Netanyahu into taking an agreement with the Palestinians seriously. The president began by demanding a total freeze on settlement construction. The Israeli prime minister outmanoeuvred and humiliated Obama, and carried on as before.

If the US president wants to revisit the fight now he's been re-elected, it would not do any harm to have the ICC hovering in the background.