A month is a long time in American politics – or so it would seem judging by the growing split among US Democrats over the Israel-Hamas war. In the days immediately after Hamas attacked Israel on 7 October, killing 1,400 people and taking more than 240 hostages, Democrats across the board in America offered unequivocal support for Israel and its right to self-defence.

That was then. Now, support for Israel’s actions has plunged the party into an increasingly vitriolic internal battle that is pitting former political allies against each other. The festering divisions in the American left running along ideological, generational and racial lines are set to deepen as the conflict drags on and the humanitarian crisis in Gaza escalates.

Israel is the one foreign policy issue that now splits the Democratic party like no other

Some in the party are calling for an immediate ceasefire in Gaza while others continue to stand firm in support of Israel’s military actions. Positions are becoming more and more entrenched, and the insults are flying, becoming uglier with each day that passes.

The tensions burst into the open earlier this week on the House floor, when 22 Democrats joined forces with the Republicans on Wednesday to censure the Democratic congresswoman Rashida Tlaib, a Palestinian American, for her rhetoric on the conflict. The censure motion accused Tlaib of ‘promoting false narratives’ about the Hamas assault on Israel. Some of her own party colleagues said she was ‘calling for the destruction of the state of Israel’.

Emotions were running high throughout the session. ‘I can’t believe I have to say this, but Palestinian people are not disposable,’ she declared, accusing her opponents of trying to ‘silence’ her.

The unprecedented rebuke of Tlaib came in the wake of video footage featuring her, shared on social media, that included a clip of pro-Palestinian protesters chanting ‘from the river to the sea’, a slogan condemned by Jewish leaders as anti-Semitic. Tlaib, rather ludicrously, has suggested that the phrase is an ‘aspirational call for freedom, human rights, and peaceful coexistence’. It really isn’t that, and Tlaib should know better than seeking to defend it as such.

Tlaib’s supporters were furious with those who supported the censure resolution. Cori Bush, a former Black Lives Matter activist who represents Missouri, accused House members of putting ‘targets on the backs of actual people, most of whom are Black or Brown’.

The fissures in the party are now spilling into public view. Debbie Wasserman Schultz, a prominent Florida congresswoman, was damning last month about party colleagues who wouldn’t back a resolution affirming support for Israel in its war against Hamas: ‘Someone who votes against this, I would think, doesn’t have a soul.’ Some in the Congressional Black Caucus were quick to hit back, telling her that referring to people of colour as ‘soulless’ is a trope that was used to justify slavery. These are cracks too deep to be papered over easily.

The American left is facing a long overdue reckoning. Support for Israel used to be one of the few areas of bipartisan consensus: Democrats and Republicans fought tooth and nail over most things but tended to speak as one on Israel. No longer.

Israel is the one foreign policy issue that now splits the Democratic party like no other. This divide has become more pronounced in the last decade or so, as the party base shifted more to the left and Israeli politics moved steadily rightwards.

The progressive wing of the party is now much more openly and defiantly critical of Israel. Polling from Gallup, published in March, showed that for the first time in more than two decades, Democrats sympathised with Palestinians more than Israelis. Research also suggests that younger members of the party are much less supportive of Israel than their elders.

The splits in his party are a dangerous challenge for President Joe Biden. His initial handling of the crisis was sure-footed and he was crystal clear in his strong support for Israel and its right to self-defence. But there are signs of a gradual shift: the backing for Israel is still there but it is increasingly accompanied by language raising concerns about the unfolding humanitarian crisis in Gaza and the need for Israel to protect civilians.

Even so, Biden is finding himself increasingly at odds with a significant chunk of his own party. The divisions in the ruling party could not come at a worse time: America is struggling to forge an international consensus on what happens to post-war Gaza as well as contain the ripple effects of an increasingly dangerous and unpredictable war in the Middle East. Bickering and divided Democrats back home can only diminish Biden’s attempts to project strong US leadership on the international stage at this critical time.