The letter released on Thursday adds to the growing calls from sources close to the Biden administration to push for an end to the war.

“As President of the United States, you have significant influence in this perilous moment,” the letter, first reported by Vox, said.

“You must call for a ceasefire, hostage exchange, and de-escalation, and take concrete steps to address the conditions of occupation, apartheid, and ethnic cleansing at the root of the horrific violence we are witnessing now.”

While the Biden administration and Congress remain steadfast in their support for Israel, staff members, grassroots organisations and activists have been expressing growing opposition to the war.

The American Postal Workers Union, which represents US Postal Service employees, also backed calls for a ceasefire on Thursday.

“We call on our government, which is the primary foreign benefactor of the Israeli government, to use all its power to protect innocent lives and to help bring about peace in the region, and not use our tax dollars for more war,” the union said in a statement.

“We join the calls for an immediate ceasefire, the release of hostages, and urgently needed massive humanitarian aid to the people of Gaza. The cries of humanity demand nothing less.”

Growing calls

The two statements follow earlier efforts from within the government to push for an end to hostilities.

Last week, employees at the United States Agency for International Development (USAID) circulated a letter calling for an immediate ceasefire, and by Wednesday, it had surpassed 1,000 signatures.

Hundreds of Congress staffers also staged a walk-out on Wednesday to demand an end to the war.

Thursday’s letter by people who worked on Biden’s campaign highlighted the mounting death toll in Gaza and the mass displacement of residents in the territory’s northern reaches, noting that scholars have raised alarm about the risk of genocide in the conflict.

The Democratic staffers also said they were “horrified by the devastating Hamas attack against Israeli civilians on October 7″.

United Nations agencies and rights groups have also urged a ceasefire, with UN chief Antonio Guterres warning that Gaza is becoming a “graveyard for children”.

But early Thursday, Biden ruled out any definitive stop to the conflict. When reporters asked about the possibility of a ceasefire in Gaza, the US president said, “None, no possibility.”

Biden has voiced unconditional support for Israel and requested more than $14bn in additional assistance for the country since its war in Gaza started on October 7, angering US progressives, Palestinians, Arabs and Muslims.

Last month, the US president sparked outrage among Palestinian rights supporters when he cast doubt over the death toll in Gaza, saying that he has “no confidence in the number that the Palestinians are using”.

Rights experts and fact-checkers defended the numbers, which are released by the Palestinian Health Ministry in Gaza based on hospital and morgue records. They explained that, in previous conflicts, the Health Ministry’s numbers matched the findings of independent researchers.

A senior State Department official also said on Wednesday that the actual Palestinian death toll may be even higher than the official numbers.

“In this period of conflict and conditions of war, it is very difficult for any of us to assess what the rate of casualties are,” Barbara Leaf, assistant US secretary of state for Near Eastern affairs, told lawmakers.  “We think they’re very high, frankly — and it could be that they’re even higher than are being cited.”

The Health Ministry has also said that its current statistics do not account for people who remain under the rubble or who were buried without being registered.

‘His legacy will be genocide’

When Biden ran for president, his supporters often portrayed him as a “decent” man aiming to restore unity in the US after the presidency of Donald Trump.

Biden has suffered personal grief in his life, having lost his wife and young daughter in a car accident in 1972 and his son Beau, a politician and army veteran, to cancer in 2015.

The campaign staffers’ statement called out the US president for appearing to play down — if not dismiss — civilian casualties in Gaza.

“Mr President, you have spoken intimately about the unbearable pain and grief of losing a child,” the letter said. “We were shocked and saddened to see you justify the death of Palestinian children as ‘the price of waging a war’.”

Biden made that comment while questioning the Palestinian death count on October 25, in an appearance before reporters at the White House. “I’m sure innocents have been killed, and it is the price of waging war,” he said.

As the US president faces pressure from his own base, his approval ratings among Democrats are slumping. He is also seeing an enormous drop in support in Arab communities.

A recent New York Times poll showed Biden losing to Trump — the likely Republican nominee in the 2024 race — in five key swing states: Nevada, Georgia, Arizona, Pennsylvania and Michigan.

Heba Mohammad, a Palestinian American staffer who worked for the Biden campaign in another swing state, Wisconsin, warned that the carnage in Gaza may become what people remember him for.

“President Biden has the ability and responsibility to save lives and reduce human suffering,” she said in a statement accompanying the letter. “If he doesn’t act swiftly, his legacy will be genocide.”