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Rep. Devin Nunes

A week has passed since lawyers for the anonymous whistleblower who set off the impeachment inquiry extended an offer to House Republicans to make the whistleblower available to answer written questions under oath.

Updated at 9:31 a.m. ET

The latest political sandstorm in the Russia saga is over four pages of paper that have never seen the light of day. Here's what you need to know to make sense of what's going on with this story.

1. What exactly is this memo that everyone is talking about?