In an ever-more polarised Washington DC, there are only a handful of issues where Democrats and Republicans are able to work across the Congressional aisle. Support for Israel, however, is one of them.

That bipartisan consensus was on display again a couple of weeks ago as the Taylor Force Act — a bill proposed by Republican Senator Lindsey Graham that aims to slash US funding for the Palestinian Authority until it stops paying salaries to terrorists serving time in Israeli jails — sailed though the Senate Foreign Relations Committee.

The following day, Senator Chuck Schumer, the Democrats’ leader in the Senate, announced that he would formally co-sponsor the bill, all but guaranteeing its passage in America’s upper house. As Mr Schumer made his announcement, Steny Hoyer, the Democrat whip in the House of Representatives, was in Jerusalem with 19 of his congressional colleagues. There was, he declared, no weakening in the party’s backing for the Jewish state.

But is the ground beneath the party’s leadership in Washington cracking?

At the beginning of the month, the Democratic Socialists of America (DSA) held their annual conference in Chicago.

A left-wing group which often works with the Democratic party, the DSA was virtually moribund for many years but has experienced something of a revival over the past year,

They have been buoyed not simply by the presidential candidacy of self-proclaimed democratic socialist Bernie Sanders — though the Vermont senator is not a member of the DSA and remains an independent — but also by the surge in membership that many left-wing groups have experienced in the wake of Donald Trump’s election.

The organisation’s ranks have recently tripled to 25,000, with new chapters opening in conservative states easily won by the president last November, including Texas, Idaho, Kansas and Montana.

The DSA’s heritage is intimately tied to many of America’s great Jewish intellectuals. The heir to Eugene Debs’s Socialist Party of America — which provided a distinctly warmer welcome to Jewish immigrants at the turn of the century than either the Democrats or Republicans — one of the DSA’s leading thinkers was the literary critic and editor of Dissent magazine, Irving Howe.

Despite this proud history, the national convention overwhelmingly passed a strongly worded pro-BDS motion as delegates chanted: “From the river to the sea, Palestine will be free”.

It was also telling that delegates at the convention rejected a motion to break with the Democratic party and formally establish a third party with the hope of persuading Mr Sanders to be their nominee in 2020.

Since Hillary Clinton’s defeat, her party has come increasingly under the sway of Mr Sanders and his supporters and, mirroring the Republicans sharp right turn after Barack Obama’s election, is now tilting towards the left.

Ultimately, this spells trouble for the party’s relationship with Israel.

Thanks to Mrs Clinton’s control of the committee that drafted the Democratic platform ahead of last summer’s convention, attempts by Mr Sanders’s delegates to push more condemnatory language about Israel were thwarted.

With Mrs Clinton’s centrist politics increasingly under assault, however, the left may well have the upper hand by 2020. Certainly, liberal Democrats — a key group in the primary elections that pick the party’s candidates — seem to be drifting away from their previous steadfast support for Israel.

Polling by the Pew Research Group earlier this year found that, while 74 per cent of Republican voters say they sympathise more with Israel than the Palestinians, only 33 per cent of Democrats think likewise.

Democrats are now — probably for the first time ever, believes Pew — almost equally split between sympathising more with Israel (33 per cent) and with the Palestinians (31 per cent).

This change is being driven by liberal Democrats: at the turn of the century, they favoured Israel by 30 points; today, they favour the Palestinians by 12 points.

The impact of this shift will eventually be felt in Washington — and many Democrats who support the Jewish state will find themselves caught between their principles and a grassroots left keen to flex its muscles. It is an uncomfortable position to be in, as any pro-Israel Labour MP in Britain is able to attest.