President Barack Obama and members of Congress discussed and debated the Affordable Care Act for several months before it became law in 2010. But somehow there is still a huge question about the mechanics that the U.S. Supreme Court now has to answer.

Can people get federal tax subsidies to buy health insurance, no matter what state they live in?

The law does not specifically say that everyone can. In fact, conservatives like Oklahoma Attorney General Scott Pruitt have argued for the past two years that the law clearly says people can only get financial aid if their state set up its own health insurance marketplace, known as an exchange.

This year, only 13 states and the District of Columbia have their own exchanges. People in Oklahoma and 36 other states who buy insurance on the individual market do so through an exchange — a marketplace — operated by the federal government.