President Trump’s One Big Beautiful Bill Act, which slashes taxes for the wealthy and services for the poor and middle class, will have an ugly fiscal impact in Marin. A report presented to county supervisors this week painted a bleak picture of cuts to health care, social services and climate programs that will be particularly brutal for the county’s immigrant community. At risk are a substantial portion of federal subsidies for the county’s Medicaid, welfare and nutrition assistance programs, which totaled $36 million last year. Affordable Care Act subsidies will also be sharply reduced. State and local agencies are still assessing the impact of the bill, which will be implemented in stages, but it will undoubtedly be great, said Ahmed Ismail, the county’s chief fiscal officer. “The biggest impacts will fall on our most vulnerable residents, including low-income families and immigrants,” he said. “As federal support is reduced, counties like ours will be asked to step in more and do more.” More than one in three Californians, including 54,000 Marin residents, rely on Medi-Cal, the state Medicaid program. Another 1.8 million rely on the A.C.A., and 6.6 million are enrolled in Medicare. As these programs are rolled back, more residents will turn to county-funded health programs as other options disappear, Mr. Ismail said. “Food insecurity will grow, with greater reliance on local food banks… Emergency and crisis care will replace preventative care. Delayed and foregone care will create backlogs and worsen health conditions. And finally, behavioral health needs will rise as untreated primary care issues spill over into mental health and crisis services.” Representatives of local health clinics urged supervisors to step up but predicted that neither the state nor county could compensate for the dramatic losses. “Your support of the Petaluma Health Centers, West Marin clinics and all the people we serve is not just commendable, it’s essential,” said Sveinn Sigurdsson, chief administrative officer of Petaluma Health. “With your help, we will continue to say yes to health care, regardless of ability to pay, yes to serving communities that are too often overlooked, and yes to programs that not only treat illness but prevent it.”