At the beginning of the year, Israel’s foreign minister Yair Lapid reflected on the diplomatic challenges for 2022.

“We think that in the coming year, there will be debate that is unprecedented in its venom and in its radioactivity around the words ‘Israel as an apartheid state’,” he told Israeli journalists. “In 2022, it will be a tangible threat.”

Lapid pointed to two United Nations investigations he said were likely to conclude that Israel’s governance of occupied Palestinian territory amounts to the crime of apartheid under international law.

Several Israeli and international human rights organisations have reached exactly that view, including Amnesty International with the release of a report this week, Israel’s Apartheid Against Palestinians: a Cruel System of Domination and a Crime Against umanity.

Israel is also facing an international criminal court investigation into actions in the occupied territories, such as the confiscation of Palestinian land to build Jewish settlements, that Amnesty International and others have said breach international laws against apartheid.

But Israel is also concerned that the breaking of the longstanding taboo in the US on comparing its rule over the Palestinians to white South Africa’s racist repression of its black population is evidence of a slower-moving – but potentially more dangerous –threat: the fracturing of once rock-solid backing for Israel within its most important ally.

The Israeli foreign ministry’s director general, Alon Ushpiz, placed protecting longstanding bipartisan support for the Jewish state in the US at the top of a list of Israel’s diplomatic priorities this year as opinion polls show eroding support among Democrats, in part driven by changing narratives about the Israeli-Palestinian conflict.

For years, polls showed that Democrats sympathised with the Israelis at twice the rate of support for the Palestinians. But since the Israeli assault on Gaza in 2014, backing for the Jewish state has fallen and support is now about evenly divided.

That change is accentuated among younger Americans, with adults under 35 far less well-disposed towards Israel than older generations.

A separate survey last June found that half of Democrats want Washington to shift policy toward more support for the Palestinians.

Support for Israeli government policies is even falling within the US Jewish community, with a poll last year finding that 25% of American Jews agreed that “Israel is an apartheid state”.

There is little evidence that Washington’s backing for Israel, including the largest amount of (mostly military) US aid given to any country, is in any immediate danger. But pro-Israel groups are increasingly concerned at the diminishing effectiveness of their attempts to portray the Jewish state as yearning for peace but confronted by Palestinian terrorism.

That claim has increasingly been challenged by what Americans can now see on social media, particularly video of Israeli attacks and maltreatment of Palestinians. Israel’s 2014 assault on Gaza – when it killed more than 2,000 Palestinians and destroyed schools and homes in response to Hamas rocket attacks that killed three Israeli teenagers – helped solidify the view of an all-powerful state unleashing destruction against a largely defenceless population.

The rise of Black Lives Matter has fuelled the drive to frame the Palestinian cause as a civil rights issue of resistance to Israeli domination.

“People can see for themselves what’s happening in a way they didn’t before,” said Sarah Leah Whitson, the former director of Human Rights Watch’s Middle East division who worked on the group’s report, A Threshold Crossed, Israeli Authorities and the Crimes of Apartheid and Persecution.

“It’s made it harder, particularly in the United States, for the emotional defenders of Israel, who’ve had this mythology about Israel and the kibbutz and sowing the land and this sort of fantasy of what Israel’s like, confronted with the reality of what they see in front of their faces.”

Israel’s attempts to push back against the shifting narrative have been undermined by its own actions, including the passing of the “nation state” law in 2018 which enshrined Jewish supremacy over the country’s Arab citizens. Israel’s prime minister, Naftali Bennett, and members of his cabinet have a long history of opposition to a Palestinian state.

Israel can still count on solid support at the top of the American power structure. But Democratic sympathies were not strengthened by Israel’s former prime minister Benjamin Netanyahu, who was openly hostile to President Barack Obama while publicly aligning with the Republican leadership in Congress.

His embrace of Trump’s “peace plan” two years ago further alienated some Democrats who denounced it as a smokescreen for Israeli annexation in the West Bank that would create Palestinian enclaves reminiscent of “Bantustan”, black homelands in South Africa.

Daniel Seidemann, an Israeli lawyer who has spent decades exposing Israel’s land grab and settlement policy in occupied East Jerusalem, recently travelled to Washington to gauge Israel policy.

“The sands are shifting in the United States, in the Congress, in public opinion, and in the American Jewish community, and the apartheid discourse is part of it. There is a centre but that centre is not going to hold,” he said.

“Increasing numbers of people abroad are beginning to see Israel as an apartheid state and a pariah state, and Israelis are increasingly fearing that.”