Another Bluedog Democrat to retire.

Rep. Bart Gordon (D-Tenn.) announced he’s not running for re-election this morning, becoming the fourth House Democrat from a politically-competitive district to announce retirement plans in the last month.

“I feel honored that the people of Middle Tennessee have allowed me to serve them for the past 25 years,” said Gordon. “Every decision I have made in Congress has been with their best interests in mind. I hope the people here at home feel that I have served them as well as their good advice and views have served me.

“When I was elected, I was the youngest member of the Tennessee congressional delegation; now, I’m one of the oldest. In fact, I have members of my staff who weren’t even born when I took office. That tells me it’s time for a new chapter.”

Gordon becomes the tenth House Democrat to retire this election cycle, with over half of them in districts Republicans plan to aggressively contest. His announcement follows the post-Thanksgiving retirements of Reps. Dennis Moore (D-Kan.), John Tanner (D-Tenn.) and Brian Baird (D-Wash.) – all of whom represent politically-competitive districts.

Gordon hadn't faced much political competition in recent years, winning his seat with more than 60 percent of the vote since 2000.

But internal Republican polls showed Gordon in serious danger of losing his seat next year, running for re-election in a Republican-leaning seat. Gordon didn't help his re-election prospects supporting the Democratic cap-and-trade energy bill and by initially supporting health care reform legislation in committee — even though he changed his mind and voted against the bill on the House floor last month.

“Tennessee is now the place where Democrat congressional candidacies go to die," said National Republican Congressional Committee spokesman Andy Sere. "Within a matter of weeks, four Volunteer State Democrats have abandoned their campaigns for Congress because voters there are rejecting the Obama-Pelosi agenda."

The race to succeed Gordon, in a middle Tennessee district that John McCain carried by 25 points, immediately jumps to the top of the Republican pickup opportunity list. McCain won 62 percent of the vote here in 2008, while former President George Bush won the district with 60 percent in 2004.

State senator Jim Tracy, former Rutherford County party chairwoman Lou Ann Zelenik, military veteran Dave Evans and businessman Kerry Roberts are all vying for the Republican nomination – though other candidates may enter the race.

Tracy, who previously told POLITICO that he was likely to run against Gordon, is now entering the open-seat race, according to a GOP operative familiar with his plans. Tracy represents much of the district's population base in the state Senate and is emerging as national Republicans' favored candidate in the primary.