Massachusetts Democratic Rep. Stephen Lynch's all-but-certain decision to run in the soon-to-be-official special election to replace Sen. John Kerry (D) means the stage is set for a matchup between a conservative Democrat and the liberal dean of the state's congressional delegation.

With Kerry set to cruise to confirmation as President Obama's next secretary of state, the Democratic race to replace him was beginning to look like it was Rep. Ed Markey's for the taking. The longtime congressman had lined up the support of Senate Democrats' campaign arm, along with a growing list of prominent Bay State Democrats.

It all wasn't enough to scare away Lynch, who looks set to enter the race. A source familiar with his thinking told The Washington Post he is running. Lynch later told the Boston Globe -- which also reported he was running -- Friday afternoon that he hasn't made up his mind yet.

At this point, Markey's money and high-profile supporters would make him the clear favorite. But Lynch is no pushover, having defied the odds in state legislative races all the way up to his first bid for Congress.

The competition would set up a stark ideological contrast. On one side is Lynch, who is no favorite of liberals. His opposition to Obama's health-care reform measure and his antiabortion rights stance will surely be fodder for attacks from the left.

On the other is Markey, a well-funded, long-serving pol who will have the support of the state's liberal base and the Democratic Party's leading figures, including Kerry.

"This is an uphill fight for [Lynch] in a Democratic primary," said Bay State Democratic strategist Mary Anne Marsh. But, she added, Lynch is "clearly going to make Markey earn this."

Among the questions for Lynch is whether he is capable of building a wide enough base of moderate Democrats and can keep pace with Markey in the money race. How much support Lynch can expect from labor will be another major question.

We don't yet know the answers to these questions. But one thing we do know is the race to replace Kerry just got a whole lot more interesting.

And now, to the Line!

We're moving Massachusetts and Georgia onto the line, while Minnesota and Colorado are coming off.

10. Massachusetts (Democratic-controlled): We still don’t know for sure whether former senator Scott Brown (R) is in or out, which prevents us from ranking this any higher. Assuming he does run, though, the GOP has a fair chance – or better. In fact, the earliest poll of the race suggests Brown would start out with a big lead over Markey, 48 percent to 30 percent. One thing to keep in mind: Neither Lt. Gov. Tim Murray (D) nor Attorney General Martha Coakley (D) are running for governor in 2014. The lack of an obvious Democratic frontrunner in that race could prompt Brown to take an awful long look at it entering that contest instead. (Previous ranking: N/A)

9. Georgia (Republican-controlled): Republican Sen. Saxby Chambliss's retirement opens the door for Democrats here, and Atlanta Mayor Kasim Reed is a potential candidate to watch. Meanwhile, the GOP field could be a crowded, unpredictable, and expensive battle of conservative credentials, which could weaken the eventual nominee. But make no mistake, while Democrats have new signs of life in Georgia, winning the conservative state remains a heavy lift. (Previous ranking: N/A)

8. Kentucky (R): This is one of just two GOP seats on this list, but we can also see Senate Minority Leader Mitch McConnell (R-Ky.) skating to reelection. That’s because Democrats have their work cut out for them in recruiting. Much of the early buzz surrounds actress Ashley Judd, but as (apparently) a pretty standard-issue liberal, it's not clear that she's an ideal candidate in a state that gave Obama just 38 percent of the vote last year. (Previous ranking: 9)

7. Montana (D): The GOP tilt of the state prompted us to keep this race where it is. That said, this isn't Democratic Sen. Max Baucus's first rodeo. And he doesn't have to look very far for someone who has defied the heavy GOP influence in Montana to keep his seat, with fellow Democratic Sen. Jon Tester doing just that in 2012. Republicans will need to find a strong candidate for this race, as the last election showed that having an "R" in front of your name is not enough here. (Previous ranking: 7)

6. Arkansas (D): Sen. Mark Pryor (D) will receive an early boost in March when Bill Clinton helps him raise money. But the state's GOP lean will make Pryor's task a tough one. On the Republican side, Lt. Gov. Mark Darr looks like he is set to run, but keep an eye on rising conservative star and freshman Rep. Tom Cotton (R), who many Republicans feel would be a stronger candidate. (Previous ranking: 5)

5. Louisiana (D): Rep. Bill Cassidy (R-La.) has been taking steps toward a challenge to Sen. Mary Landrieu (D-La.) in 2014, traveling parts of the state outside his district. GOP recruits against Landrieu have largely been a disappointment. Cassidy will have to prove himself, but these days a Southern Democrat is a vulnerable Democrat, and Cassidy should have a good chance to beat Landrieu if he can run a decent campaign. (Previous ranking: 6)

4. North Carolina (D): A recent poll from Democratic-leaning automated pollster Public Policy Polling shows Democratic Sen. Kay Hagan's approval rating is underwater, but she nonetheless leads potential GOP competitors. If Republicans can find the right candidate, Hagan will face a tough road to reelection. (Previous ranking: 4)

3. Alaska (D): Keep an eye on Democratic Sen. Mark Begich's votes on gun control. He has an "A" rating from the NRA, and with an election looming, will be one of the toughest Senate Democrats for gun control advocates to win over. Begich's spokesman has already said he does not favor new laws to expand the background check system. (Previous ranking: 2)

2. West Virginia (D): We're moving this race up on our list following the retirement of Sen. Jay Rockefeller (D), who is a household name in the state. While his ties to Obama would have caused him some problems, the uncertainty about who Democrats will nominate paired with the strength of the likely Republican nominee, Rep. Shelley Moore Capito, now makes this a top GOP pickup opportunity. (Previous ranking: 3)

1. South Dakota (D): Sen. Tim Johnson (D-S.D.) doesn’t sound like a guy who’s gearing up for a reelection campaign, but he hasn’t made anything official. Given former governor Mike Rounds’s early entry in this race, it would behoove Johnson to decide sooner than later, in order to give his replacements as much time as possible to compete financially with Rounds. Johnson says he’ll decide this spring. Possible replacements include former congresswoman Stephanie Herseth Sandlin and Johnson’s son, U.S. Attorney Brendan Johnson. Rounds might be favored either way. (Previous ranking: 1)