Dearborn, Michigan - Joe Biden scored an easy win in Michigan's presidential primary Tuesday but was dealt a stinging rebuke over the war in Gaza in an Arab American-led protest that raised concerns over his bid to win the swing state in November's election.

There was little suspense over the outcome for both parties, with the president almost unopposed in the Democratic nominating contest and his predecessor Donald Trump declared the victor the Republican vote as polls were closing.

But tens of thousands of Democrats in a swing state crucial to Biden's reelection hopes ticked the "uncommitted" box as part of a push by the Listen to Michigan campaign to jolt the president into backing off from his support of Israel's brutal war on Gaza.

With some 99% of polling stations reporting, the "uncommitted" share accounted for over 100,000 votes – some 13% – far above the final totals in each of the last three election cycles.

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Biden released a statement thanking voters, touting his record on working for Michigan's middle class and acknowledging that there was "much left to do" – but made no mention of the Gaza conflict and ignored the protest vote.

Listen to Michigan had set a modest goal of rallying 10,000 uncommitted voters in its aim to censure the president over US military funding for Israel's assault, which has killed some 30,000 people in Gaza and is raising increasingly widespread concerns of genocide.

"President Biden has funded the bombs falling on the family members of people who live right here in Michigan – people who voted for him, who now feel completely betrayed," the campaign said in a statement claiming victory.

Though they never threatened Biden's win, the significant number of "uncommitted" votes could set off alarm bells ahead of the November general election, when Biden cannot afford to see his coalition eroded in the swing state.

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The US Census Bureau estimates the statewide population claiming Middle Eastern or North African descent at 310,000, although the Arab American Institute says that figure is likely a significant undercount.

The organization estimates a nationwide Arab American population of 3.7 million and says the vast majority – more than 80% – are US citizens with the right to vote.