From the debates to Iran, it’s been a busy week in American politics. Here are some of the biggest stories you might have missed (and some links if you’d like to read further).

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The first Democratic debate lineup was announced.

The Democratic National Committee revealed which 20 candidates would be in the first two debates in Miami this month. Steve Bullock, Seth Moulton and Wayne Messam will be left out.

They didn’t make the cut, in part, because they failed to reach 1 percent in three qualifying polls. Their exclusion illustrates the challenge of using polls at this early stage to make sense of the race, let alone to decide whom to include in a debate.

Joseph R. Biden Jr. will share the stage with Bernie Sanders on one night, and Elizabeth Warren will face off against Beto O’Rourke on another. Though there are prominent candidates on both nights, it seems clear that Ms. Warren will be in a good position to command the first evening.