US President Joe Biden comfortably won the Democratic primary in Michigan on Tuesday, despite significant defections from a group of voters in his party angry at his support for Israel’s war in Gaza.

Progressive activists and Arab-American leaders had urged Michigan Democrats to vote “uncommitted” rather than support Biden, in a warning sign for his expected re-election bid against Donald Trump in a crucial swing state.

The dissent within his own party in Michigan has emerged as one of the biggest political challenges for Biden’s campaign in recent weeks, raising fears among some Democrats that he will struggle to unite their centre-left coalition around his candidacy in November.

The backlash over Gaza has also thrust foreign policy into the heart of the race for the White House, along with other top issues such as immigration, the economy, the future of US democracy, and the character of the candidates.

At 6am Eastern time on Wednesday, with 98 per cent of Democratic votes counted across Michigan, Biden had won 81.1 per cent, while 13.3 per cent had picked “uncommitted”. Long-shot candidates Dean Phillips and Marianne Williamson had 2.7 per cent and 3 per cent respectively.

In a statement late on Tuesday after the vote, Biden did not mention the war in Gaza, but pointed to his economic policies and efforts to protect reproductive rights. “This fight for our freedoms, for working families, and for Democracy is going to take all of us coming together. I know that we will,” he said.

Separately in Michigan, Trump notched up another comfortable victory in the race for the Republican presidential nomination against Nikki Haley, his former US ambassador to the UN, bringing him another step closer to locking up his party’s support.

At 6am, Trump had won 68.2 per cent of the Republican vote, while Haley had won 26.5 per cent — showing that he also faces defections from within his party.

“We win Michigan, we win the whole thing,” said Trump after the primary vote, referring to the presidential election in November.

Haley vowed to continue her campaign through to Super Tuesday on March 5.

The protest on the Democratic side is a reaction to Biden’s continued support for Israel during the conflict in Gaza, where almost 30,000 people have died, according to Palestinian officials, since Israel declared war on Hamas in response to the militant group’s October 7 attack.

“President Biden has funded the bombs falling on the family members of people right here in Michigan,” said Layla Elabed, campaign manager for Listen to Michigan, a group behind the “uncommitted” protest vote. “Thousands of Michigan Democrats who voted for Biden in 2020 now feel completely betrayed.”

Michigan is a battleground state that has been decided by narrow margins in recent election cycles. Biden defeated Trump there in 2020 by just 150,000 votes, while Trump defeated Hillary Clinton four years earlier by fewer than 11,000 votes.

Just over half of the people living in Dearborn, a suburb of the state’s biggest city Detroit, are Arab American, according to the latest census. About 140,000 Arab Americans voted in Michigan in the 2020 presidential election.

Rashida Tlaib, a Palestinian-American member of Congress whose district includes much of Dearborn, was among those encouraging Democrats to lodge a protest vote. Elabed, the campaign manager for Listen to Michigan, is Tlaib’s sister.

“I was proud today to walk in and pull a Democratic ballot and vote uncommitted,” Tlaib said in a video posted to social media on Tuesday. “When 74 per cent of Democrats in Michigan support a ceasefire, yet President Biden is not hearing us, this is the way we can use our democracy to say, listen.”

Biden has long been a staunch supporter of Israel. But he has been increasingly critical of Israeli Prime Minister Benjamin Netanyahu in recent weeks and told reporters on Monday that he was hopeful a temporary ceasefire could begin in Gaza as soon as next week.

Recent opinion polls have put Trump ahead of Biden in a hypothetical match-up in Michigan. An Emerson survey published last week showed him leading by a four-point margin in the state.

Several of Biden’s public events have been interrupted by pro-Palestinian protesters in recent weeks, and the death at the weekend of a US airman who set himself on fire outside the Israeli embassy in Washington made headlines across the country.

Gretchen Whitmer, Michigan’s Democratic governor who was re-elected in 2022, is a co-chair of Biden’s re-election campaign and has been among his loudest defenders in the state.

As the results trickled in on Tuesday night, Whitmer said she was “proud” of her state’s “rich diversity of backgrounds, ideologies and cultures” but said there was a “stark choice” ahead. “It’s time to come together and go full steam ahead to November for Joe Biden and Kamala Harris, and we will continue getting the word out every day about what’s at stake,” she said.