“I’m dreading the unpredictability,” said John J. Lynch III, Main Line’s president and chief executive.

Over all, the health law has improved the financial outlook of Pennsylvania hospitals significantly, even though the state was a year late in expanding Medicaid. The former governor, Tom Corbett, a Republican, initially balked, and the program did not expand here until 2015. Still, hospital operating margins statewide increased to about 5.5 percent on average in 2015, from 4.25 percent in 2014, according to the Hospital and Healthsystem Association of Pennsylvania. The amount of care provided to patients who cannot pay dropped by 8.6 percent on average.

North Philadelphia, where Temple is based, is among the poorest neighborhoods in the nation. Many of its residents live in deep poverty, a census designation that means their income is less than half the federal poverty level of $24,300 for a family of four. That helps explain why Temple is so dependent on Medicaid revenue, and the high stakes of repeal here.

Under the health law, hospitals that served a large number of poor and uninsured patients agreed to a series of funding cuts in exchange for getting far more patients with insurance coverage. Temple has lost about $11 million so far in these federal funds, known as disproportionate share payments, Mr. Lux said.

But like other hospitals in the 31 states that expanded Medicaid under the law, it has made up that revenue in part through the Medicaid expansion. It recorded about 13,000 more visits from patients with Medicaid coverage in 2015, the first year Pennsylvania expanded Medicaid eligibility, and at least as many this year. Still, Temple is barely turning a profit: It had operating income of $3.6 million in the fiscal year that ended June 30, despite revenue of $1.7 billion.

“You still have a pretty fragile enterprise,” Mr. Lux said, noting that Medicaid pays hospitals and doctors far less than Medicare and private insurance. “Our current state of stability could be broken pretty quickly.”