Biden faces no serious opposition to being nominated to run for a second term in the White House.
But as the civilian death toll mounts in the conflict between Israel and Hamas, he has seen support erode among Muslims and Arab Americans, a bloc crucial to his narrow 2020 victory over Trump in Michigan.
Activists in the key midwestern battleground -- where Biden's winning margin four years ago was a mere 150,000 votes -- want Michigan residents to vote "uncommitted" in protest, pressuring the president to back off from his Israel support and call for an immediate ceasefire.
"President Biden has funded the bombs falling on the family members of people right here in Michigan -- people who voted for him, who now feel completely betrayed," said Layla Elabed of the "Listen to Michigan" campaign.
The group aims to amass 10,000 "uncommitted" voters to deliver a "powerful, unequivocal message" that funding and supporting the war is "at odds with the values of the Democratic Party."
Biden is cruising to the Democratic nomination, with his main would-be rival, Minnesota congressman Dean Phillips, polling in single digits.
But activists deny that the "uncommitted" campaign is merely symbolic, given their importance in an election decided on small margins.
"Ten thousand votes is about the same as Donald Trump's margin over Hillary Clinton in 2016," Elabed said.
The war started when Hamas attacked Israel on October 7, resulting in the deaths of about 1,160 people in Israel, mostly civilians, according to an AFP tally of official Israeli figures.
But concern has mounted amid the high civilian death toll in Israel's retaliatory campaign, now at almost 30,000, according to the health ministry in Hamas-run Gaza.
'Stark numbness'
White House officials have portrayed Biden as frustrated with Israeli prime minister Benjamin Netanyahu.
Still, US weapons have continued to flow to Israel, even as efforts continue to broker a second pause in fighting.
Biden has asked Congress for billions of dollars in additional military aid and his government has vetoed multiple UN Security Council calls for a ceasefire.
A similar write-in campaign calling for a ceasefire during the New Hampshire primary went nowhere, but Michigan has a significantly larger Muslim and Arab population.
"With every day that passes, every minute that the president fails to do the right thing, the belief that I and so many others have invested in him dwindles," Abdullah Hammoud, the mayor of the heavily Arab American Detroit suburb of Dearborn, wrote in The New York Times last week.
"With every American-made bomb that Israel's right-wing government drops on Gaza, a stark numbness coats everything, restricting any space for belief to grow."
On the Republican side, Trump has swept the early voting states and Michigan is not expected to interrupt his march to the nomination.
His sole remaining challenger, former UN ambassador Nikki Haley, lost her home state of South Carolina to Trump at the weekend but has refused to quit, saying she doesn't believe Trump can defeat Biden.
Haley suffered another blow Sunday when the wealthy Koch family network said it was halting its donations to her campaign.
Both parties hold votes on Tuesday, although Republicans have adopted a complex hybrid system that wraps up the contest four days later via caucus-style gatherings in each of the state's 13 congressional districts.
More than two-thirds of the Republican delegates -- the individuals appointed by each state to back candidates at the party's summer nominating convention -- will be awarded on March 2.
