“The Affordable Care Act sets up new insurance exchanges through which people can buy coverage, and it provides tax credits to help low-income people with that purchase. The law says each state should set up its own exchange but also directs the federal government to set one up in any state that does not. The IRS is planning to provide tax credits in state-based and federally run exchanges. Issa and other conservatives say the subsidies should only be available in state exchanges — not the federal fallback.”