Via The Hill:

A key Democrat on the House Transportation and Infrastructure Committee said Tuesday that he would not run for re-election next year. Rep. Jerry Costello (D-Ill.), the ranking member of the transportation panel's Aviation Subcommittee and a ten-term Congressman, will not seek another term in the House of Representatives next year, his office confirmed to The Hill. [...] A spokesman for Costello told The Hill that the congressman would release a statement about his decision to leave office later Tuesday and hold events in his district, the Illinois 12th.

This is somewhat surprising but not completely shocking. The 62-year-old Costello had been the target of a small early ad buy by the NRCC—the kind aimed at making an incumbent reconsider the rigors of seeking reelection—suggesting that perhaps they knew something was up. Republicans also have been trying to land a legitimate recruit here, which they haven't had in a while—it's been a long time since Costello has faced a competitive campaign.

One thing that most definitely doesn't appear to be a factor is redistricting. Indeed, the 12th CD saw the least change of any seat in the state, with 93 percent of Costello's old constituents inhabiting the new district. As you'd expect, the partisan composition changed very little as well, barely nudging from 54-44 Obama to 55-44.

And that definitely doesn't put it out of reach for Republicans, particularly considering that the president's 2008 numbers were inflated in his home state. (John Kerry only won the old 12th by four points.) So far, the most credible GOP candidate to announce so far is Rodger Cook, who served as mayor of Belleville for one term in the mid-90s, but Republicans are also hoping to recruit Jason Plummer, their 2010 Lt. Gov. nominee. Costello's announcement may also inspire stronger candidates to get in.

The Democratic side is more of a mystery, since this news was by and large unexpected. Costello has a son (named Jerry Costello II) who is a state representative, and he could be looking to hand the seat off to his kid. But the younger Costello has never run for office—his current job is the result of getting appointed to fill a vacancy, and only back in July of this year at that. Time is short, though. Candidates have to circulate petitions to get on the ballot, a process that begins in earnest this month, and the filing deadline is Dec. 5. What's more, Illinois has an early primary (March 20), so any race will be short. We'll keep you posted as we learn more about possible replacement candidates.