LANSING, Mich. — Christina Starks-Clay doesn’t know how “Medicare for All” would work exactly, but she’s willing to bet it’d be better than what she has now. Standing in line for U.S. Senate candidate Abdul El-Sayed’s town hall in the state’s capital in September, she whipped out her phone to pull up a screenshot. It was of the $1,000 cashier’s check she’d picked up at the bank that day to pay down a chunk of her son’s dental bills. An early childhood special education paraprofessional, she still owed $389, even with good dental insurance. Her own cleaning a few weeks before cost $600. S...