As part of its awesome attempt to make large-scale public policy based on a mixture of cynicism and ignorance, the Republican Party in its wisdom created a presciption drug benefit for Medicare recipients featuring a "doughnut hole" in the coverage. They wanted the program to be universal, and therefore popular, so every senior with any drug expenses -- even if they're really cheap -- gets some coverage. They also wanted the program to save money. But they didn't want to save money through any methods that might imperil the financial interests of pharmaceutical companies or insurance firms. So they made the benefit actually phase out as your costs grow, which is the reverse of how an insurance program is supposed to work. Then if your costs get super-high, the benefits come back.
Lurking in the middle, though, is the doughnut hole and people aren't happy about it. This is going to be important politically. The GOP essentially sold its soul to pass this bill and win votes from seniors, but they're also the bought-and-paid-for stooges of the private health care industry. If they can manage to please both constituencies at once, they're in pretty good shape. If not, then not.
Matthew Yglesias is a former writer and editor at The Atlantic.