The health insurance subsidies at the center of the US government shutdown fight disproportionately benefit areas of the country represented by Republican lawmakers, posing a potential vulnerability for President Donald Trump’s party in next year’s midterm congressional elections. Twelve million Americans in GOP-held US House districts are covered by health plans purchased through Affordable Care Act exchanges established by the 2010 law pushed through by Democratic President Barack Obama. That compares to the nine million living in Democratic-held districts.