So what happens next? Emerson's resignation will trigger a special election in her 8th District, of course, and in Missouri, nominations for specials are handled by a committee of party leaders—there's no primary. That'll give Emerson a chance to influence who her successor is, but who might that be?
The Great Mentioner has already kicked into high gear regarding possible replacements for Emerson: Analyst Jeff Smith thinks Lt. Gov. Peter Kinder, former Treasurer and failed 2010 Senate candidate Sarah Steelman, outgoing state Sens. Jason Crowley and Kevin Engler, and state party executive director Lloyd Smith could all make a go of it. Nathan Gonzales offers the same list, adding state Rep. Todd Richardson but also saying that Kinder and Smith look to have the inside track. (Both have ties to the Emerson family: Smith was Emerson's former chief of staff, and Kinder worked for Emerson's late husband Bill, whom she succeeded in Congress.) Joshua Miller tosses on a couple more: state Reps. Jason Smith and state Sen.-elect Wayne Wallingford.
And if you were wondering, I wouldn't hold out much hope for an upset possibility: We haven't crunched the most recent election results yet, but the 8th District went 60-38 for John McCain in 2008, which means it's extremely red territory. Emerson did draw a well-funded challenge from Iraq vet Tommy Sowers in 2010, but despite spending $1.6 million, he took less than 29 percent of the vote. If anything, I'd guess the 2012 numbers were worse for Team Blue, so this is really going to be a GOP-only affair. No matter what, though, we'll be following future developments here closely—because we always do!
10:20 AM PT: Here's some empirical support for the point we're trying to make about Emerson's supposed moderation. Using Prof. Keith Poole's DW-Nominate scores, it's possible to evaluate where on the spectrum of the entire House of Representatives Emerson has fallen ideologically, Congress by Congress. The number represents Emerson's rank overall, with 1 being the most liberal member:
As you can see, Emerson was always to the right of the median member (which would be defined as no. 217.5), lurching even further to the right in the 110th and 111th Congresses (when many more Democrats were elected, giving them control of the House). In the 112th, she snapped back—all the way to dead center, as it happens, because of the opposite phenomenon: So many more Republicans, particularly hyper-conservative tea partiers, won in 2010. So if you still want to call Emerson a "moderate," it's only because of the wild shift right-ward her entire party's undergone.