In what was a high-stakes primary day across five US states, the bitter Democratic Senate battle between Abdul El-Sayed and Haley Stevens in Michigan drew the most attention.But the Associated Press now projects Dr El-Sayed has ultimately won, a result that is expected to shape the Democrats' messaging to voters and how it challenges US President Donald Trump ahead of November's crucial midterms.Dr El-Sayed, a progressive epidemiologist who is pushing to cut the influence of corporate money in politics and has criticised US aid to Israel, ran as an outsider, with the support of senator Bernie Sanders and congresswoman Alexandria Ocasio-Cortez.His opponent, Haley Stevens, was a well-funded moderate, with the backing of establishment Democrat figures including Michigan's governor Gretchen Whitmer and senate minority leader Chuck Schumer.The two candidates came to represent an ideological battle between the establishment and progressives within the Democrat Party, and the Michigan contest was dominated by their views on issues like US-Israel relations and the country's future."A year and a half ago, you wouldn't have thought there was any way that Zohran Mamdani could have won [the mayor's race] in New York," David Smith, associate professor at the United States Studies Center at the University of Michigan, told the ABC."But he ran quite an extraordinary campaign, and even though there was a lot of scepticism that a Muslim who branded himself as a socialist could win a general election, could win a Democratic primary even, he won."A lot of people saw El-Sayed as a test of whether something like that can happen outside of a major deep blue city like New York."Michigan is one of the nation's key swing states, a genuinely purple region that has bounced between Democrats to Republicans and back again in presidential elections.And what happened in the August 4 primary, both at the ballot box and in the immediate aftermath, will serve as a test case for Democrats in the lead-up to 2028.Who is Abdul El-Sayed?The son of Egyptian immigrants, Dr El-Sayed, 41, was born and raised in south-east Michigan.He is the first Muslim to win a seat in the US Senate.Abdul El-Sayed was an outsider in the Michigan primary race.