A new, quick piece from me—aided greatly by Emma Roller—explains why senators insist on sending "formal letters" to each other, then releasing these letters to the media. As former Harry Reid spokesman Jim Manley explains, it's an old tradition that's been repurposed as a media-grabbing ploy.
“When you’re sending an official letter you’re killing two birds with one stone,” says Manley. “You’re not ambushing your colleague, but you’re not giving the recipient the chance to shape the message in his own direction, either. It’s far too easy to dream up a press strategy that involves writing a letter and quickly releasing it to reporters, making the recipient look pressured. There are strategists who spend whole days thinking of stuff like this.”
It's a short article, and it doesn't include the rest of the reason that congresscritters often prefer sending letters to other methods of communication. You don't just get extra media attention. You get extra attention from the recipients, who are worried about the media attention, and will work harder to put out a response. Tweet them, and you might not get anything. But members of Congress and administration officials and nominees feel compelled to respond to letters.