BIRNAMWOOD, Wis. — The land of fried cheese curds and the Green Bay Packers is among a half-dozen battleground states that could determine the outcome of the expected November rematch between President Joe Biden and former President Donald Trump — a contest in which the cost and availability of health care are emerging as defining issues. At church picnics and summertime polka festivals that draw voters of all political stripes, Wisconsinites said they’re struggling to pay for even the most basic health care, from common blood tests to insulin prescriptions. A proposal by Wisconsin’s Democrati…