WASHINGTON — Having health insurance used to hinge on where you worked and what your medical history said. Soon that won't matter, with open-access markets for subsidized coverage coming Oct. 1 under President Barack Obama's overhaul. But there's a new wild card, something that didn't seem so critical when Congress passed the Affordable Care Act back in 2010: where you live. Entrenched political divisions over "Obamacare," have driven most Republican-led states to turn their backs on the biggest expansion of the social safety net in a half century. If you're uninsured in a state that's opposed, you may not get much help picking the right private health plan for your budget and your family's needs.