Now that we’ve put the 2009 races to bed, we can start to focus heavily on 2010. Since our last update in June (available here), some critical Senate contests have undergone a transformation of sorts. We still don’t know the status of them all, since a few critical candidacy decisions remain to be made. But overall, the picture is getting clearer for the 36 Senate contests to be decided in 2010 (38 if you add the Massachusetts special to be held in January and the Texas special that might be held in May).

Let’s stress this from the outset: Democrats will almost certainly retain control of the Senate. Some bloggers aside, few of the top analysts on the Republican side question this conclusion. The GOP’s real hope is to cut the Democratic margin by a few seats, so that they can regain the power to stop legislation (assuming they stick together–a giant “if”). And this will be a significant development, should it happen. As we can already see, Senate Democrats can have difficulty passing major legislation even with 60 seats. There are some moderate Democrats who can easily defect, such as Sens. Ben Nelson (D-NE), Evan Bayh (D-IN), Mary Landrieu (D-LA), and Blanche Lincoln (D-AR). In addition, Sen. Joe Lieberman of Connecticut, an Independent who caucuses with the Democrats, is probably best described as a Republocrat. (So ironic, isn’t it, given his vice presidential bid on Al Gore’s 2000 ticket.)

Remember, any 2010 analysis must start with the seats not up in 2010. The Democrats will automatically retain 41 seats and Republicans 21–that is, these 62 seats aren’t on the 2010 ballot. Given Vice President Biden’s tie-breaking vote, Democrats need to win a mere 9 seats in 2010 to retain control, and just to begin with, they have 10 reasonably secure incumbents on the ballot. By contrast, the Republicans would have to win 30 seats to take the Senate, which would require holding all their own seats plus capturing 11 currently Democratic seats.

Let’s get real. That’s not going to happen unless there is a complete collapse on the Democratic side.

The election results in 2010 will add seats to each column. Democrats and Republicans have an equal number of seats up in 2010 (19 Democratic, 19 Republican). This gives the Democrats a large head start in retaining control since, in order to take the chamber, the GOP would have to sweep every competitive contest and make some currently uncompetitive races into major upsets.

The following chart gives you some sense of the big Senate picture for 2010. Where are the Republicans likely to make their stand, and possibly score gains?

First, the GOP has a big job on its hands just holding its seven open seats in FL, KS, KY, MO, NH, OH, and TX. Kansas is a near-certainty for Republicans, regardless of which U.S. House member is nominated in the party primary; the current sense in GOP circles is that Congressman Jerry Moran is the likely nominee over Congressman Todd Tiahrt. Florida looks likely for the GOP, though Gov. Charlie Crist is no longer the unassailable frontrunner. Conservatives much prefer former Florida House Speaker Marco Rubio, who is backed by allies of former Gov. Jeb Bush (and eventually, Bush himself). Either Crist or Rubio would be the November favorite over Democratic Congressman Kendrick Meek.

Right now, the Republican nominee would have to be slated as a slight favorite in conservative, anti-Obama Kentucky, if the nominee’s name is Secretary of State Trey Grayson–who has a serious primary battle with well-funded Rand Paul, son of Texas Congressman Ron Paul. This tiny tilt in Grayson’s direction assumes the primary doesn’t damage him too much, if he wins at all. It is too early to assess Paul as a general election candidate, though Kentucky Democrats believe they could defeat him. As for the Democrats, they have two potentially competitive candidates in Attorney General Jack Conway and Lt. Gov. Dan Mongiardo, though Mongiardo shot himself in both feet and several other places in a recent profane recorded conversation where he attacked Gov. Steve Beshear (D). Beshear had endorsed Mongiardo, but the lieutenant governor was angry that Beshear was soaking up the available campaign cash for himself. (“I am close to saying f— it all…I do not need this job…a U.S. Senate seat,” exclaimed Mongiardo.) Despite this embarrassment, Mongiardo still leads Conway in the primary. Many Democrats fondly remember that Mongiardo nearly defeated U.S. Sen. Jim Bunning (R) in 2004.

In two other states where a Republican senator is retiring, New Hampshire and Ohio, the likely GOP nominees (ex-Congressman Rob Portman and ex-state attorney general Kelly Ayotte) are somewhere between slight favorite and even-money bet, depending on whose polls and analysis you believe. Portman will likely face Ohio Lt. Gov. Lee Fisher (D), while Ayotte’s opponent will be Congressman Paul Hodes (D). Democrats are confident they can elect Fisher and Hodes, but the Buckeye and Granite States are sensitive barometers of the national drift, which could be in the GOP’s direction in 2010.

In Texas, U.S. Sen. Kay Bailey Hutchison–who is in a tough March GOP gubernatorial primary with incumbent Rick Perry–had long said she would resign her Senate seat this fall. Last weekend she announced a change in plans, saying she would resign in March, after the primary. We’ll see. If she loses to Perry, Hutchison can change her mind again, since her seat isn’t up until 2012, and many Texans would not want to lose her considerable Senate seniority. The Lone Star State normally leans Republican, but without knowing (1) exactly when–or even whether–Hutchison will resign, or (2) the identity of Gov. Rick Perry’s interim appointee, if there is one, or (3) the number of other Republicans who will run, or (4) the name of the Democratic opponent for Hutchison’s seat, it is impossible to rate. We’ll revisit this seat once the circumstances become clearer.

If 2010 becomes a solidly GOP midterm election, it’s possible, even likely, that the Republicans could sweep all seven of their open seats. But the seven represent broad exposure in widely different states, so even top Republicans privately worry that they will lose one or two.

Most GOP Senate incumbents appear robust politically, but there are two potentially competitive contests. Sen. David Vitter (R-LA) still has not overcome some of the negative effects of his prostitution scandal, and Democratic Congressman Charles Melancon might be able to make Vitter sweat. It’s also still possible that another senior Republican (such as Secretary of State Jay Dardenne) will challenge Vitter in the party primary. Vitter’s innate advantage is that the Bayou State has become increasingly anti-Obama and, post-Hurricane Katrina, tilted to the GOP. Many African-Americans who were forced to leave New Orleans and resettle in other states may never return. In 2008, Barack Obama received a mere 14% of the white vote in Louisiana–a figure that underlines the challenge for any statewide Democratic candidate.

In North Carolina Sen. Richard Burr (R-NC) has dodged the toughest Democratic challengers. Most recently, Congressman Bob Etheridge (D) turned aside national party pressure, and refused to run. Secretary of State Elaine Marshall may well be the Democratic nominee. It is a surprise that stronger Democrats aren’t jousting to be the nominee since this seat has changed party hands every six years since 1974. Burr has the burden of beating this remarkable curse. Burr’s personal and job approval ratings are consistently mediocre, not so much from built-in dislike of him as from a lack of knowledge about him. Burr is widely viewed as competent yet also very low-profile.

Obviously, Republicans hope to make up for any losses in GOP-held seats by defeating incumbent Democrats or taking open Democratic seats in Delaware, Illinois, and Massachusetts. Congressman Mike Castle (R-DE) has caused GOP hopes to soar with his decision to run the Senate race against state Attorney General Beau Biden (D), Vice President Biden’s son. The moderate Castle leads the early polls, though not by much. Delaware has become a solidly Democratic state, and the Biden family (plus the Obama White House) will pull out all the stops to support the Biden dynasty.

The GOP appears to have an even chance in Illinois with moderate Congressman Mark Kirk (R). The Democratic frontrunner is state Treasurer Alexi Giannoulias, though he has real competition from Chicago Urban League President Cheryle Jackson and possibly former Chicago inspector general David Hoffman. This is President Obama’s former Senate seat, and so as in Delaware, we can expect the White House–full of Chicago pols–to do everything within its power to keep the seat Democratic.

Republicans have no chance at all in the Bay State. The Massachusetts Democratic primary field is plentiful, and the eventual Democratic nominee is all but guaranteed to retain Ted Kennedy’s seat. Attorney General Martha Coakley is the heavy frontrunner in the December primary, with Congressman Michael Capuano and Boston Celtics co-owner Stephen Pagliuca in the hunt. Pagliuca is worth $400 million, which doesn’t hurt, but he is a former Republican with a spotty voting record–clear vulnerabilities in a Democratic primary. Capuano is running to the left of Coakley, trying to position himself as Kennedy’s ideological successor. Speaker Nancy Pelosi and former state first lady Kitty Dukakis have endorsed Capuano.

There are several Democratic incumbents who look to be vulnerable in 2010. Sen. Christopher Dodd (CT) has a plateful of problems, not least that he is identified with the banking system at a time when “banker” is even more unpopular than “lawyer”. Even Ralph Nader is considering an independent run for Dodd’s seat. For the Republicans, former Congressman Rob Simmons (R) is a respectable challenger. However, others are running for the GOP nod, and we don’t completely rule out the possibility that an out-of-the-box GOP candidate like wealthy World Wide Wresting CEO Linda McMahon could upset Simmons in the primary. A wrestler has a natural advantage in politics–and today’s Senate.

In Pennsylvania, Sen. Arlen Specter (R-turned-D) may or may not be nominated by his new party, and Democratic Congressman Joe Sestak is a tough foe, though currently behind Specter in the primary polls. Despite the backing of President Obama and Governor Ed Rendell (D), Democrats aren’t sure Specter is actually one of them–and the left is enthusiastically supporting Sestak. Awaiting either Specter or Sestak in the fall is former Congressman Pat Toomey (R), originally not considered an especially threatening contender but, if the GOP has a sweep in ’10, a possible winner.

Should Gov. John Hoeven (R) decide to challenge Sen. Byron Dorgan (D-ND), then Dorgan would face his strongest foe ever. Hoeven leads in early match-ups, though Dorgan will stress his seniority in the majority party caucus for his small state. A Dorgan-Hoeven contest would become a headliner small-state Senate battle, with many millions spent to influence a relative handful of voters.

In Arkansas Sen. Blanche Lincoln (D) cannot feel secure when early polls show her weak in a state John McCain carried in a massive landslide. Several Razorback Republican candidates are running and state Sen. Gilbert Baker may be the early favorite. National Republicans smell blood in the water here. Lincoln’s vote on health care reform is sure to make her many enemies on either the left or the right.

Probably the biggest surprise in Democratic vulnerability is Sen. Harry Reid of Nevada, the Majority Leader. It is the top Senate position that has Reid in trouble–the “Daschle effect,” referring to the 2004 defeat of Democratic Leader Tom Daschle of South Dakota. Conservative states do not seem to take well to their senators serving as a partisan battering ram for the liberal party. In early polls Reid is losing handily to two second-tier GOP candidates, real estate developer and son of a legendary basketball coach Danny Tarkanian and GOP state chair Sue Lowden, the likely eventual nominee. Yet no one should cavalierly write off the wily, long-term incumbent. Reid has raised over $11 million and already is airing reelection TV ads. He will almost certainly set a spending record for Nevada, and he will have every resource the Obama White House can supply him.

Rounding out the list of potential Democratic vulnerabilities are two appointive senators, Michael Bennet of Colorado and Kirsten Gillibrand of New York. Bennet was the surprise choice by Gov. Bill Ritter (D) to replace Obama Interior Secretary Ken Salazar (D), and while bright and wealthy, he was and is unknown to many Coloradans. Bennet is being opposed in the Democratic primary by former state House Speaker Andrew Romanoff, and the primary alone could be a tight one. Waiting for the winner in November will be former Lt. Gov. Jane Norton, who will be staunchly backed by national Republicans. Colorado was a 2008 Blue state that, like Virginia just did in its gubernatorial election, could turn Red again in ’10.

As for Gillibrand, New Yorkers seem underwhelmed by her appointment to replace Secretary of State Hillary Clinton. Some of the broad unpopularity of Gov. David Paterson, who picked Gillibrand over better known Democrats such as Caroline Kennedy, could have rubbed off. Still, national and state Democratic leaders have muscled out several tough primary challengers, leaving Gillibrand almost unopposed for the moment. The Empire State’s Republican Party has such a weak bench that Gillibrand may also get a virtual free pass in the general election. National and state Republicans are trying to convince former three-term Gov. George Pataki to toss his hat into the ring. He’d be a heavyweight contender and a real threat to Gillibrand. Yet few believe he’ll actually return to the fray.

The long and short of the 2010 Senate line-up is that Republicans have an opportunity to become relevant again by netting a few seats. They might do better. GOP leaders dream of holding every one of their seven open seats and securing their two shaky incumbents in LA and NC. Then Republican challengers could take AR, CO, CT, DE, IL, ND, NV, and PA. This would yield a Senate of 52 Democrats and 48 Republicans–still not enough for outright control but sufficient to tie the Senate in knots most of the time.

As proof that their dream scenario could happen, Republicans point the effect that a national tide can have: near-sweeps of contested Senate seats for the GOP in 1980, 1994, and 2004, as well as Democratic near-sweeps in 1986, 2000, 2006, and 2008. But in order to come close to this ideal, GOP candidates will need very favorable atmospherics in 2010 such as mediocre-to-poor ratings for President Obama, continued high unemployment, and deep disillusionment among the Democratic base. (Democrats are attempting a cure for the latter by passing health care reform.)

Democrats scoff at the GOP vision for 2010, characterizing it as somewhere between delusion and hallucination. Too many of the GOP’s own incumbents are retiring, and too many secure Democrats are on the ballot next year for a truly game-changing Senate election, they say. The odds of Republicans keeping all their open seats and protecting their endangered incumbents are quite low, insist Democratic strategists, and the chances of some currently threatened Democrats to fend off Republican challengers are high. From the Democratic perspective, Republicans will be lucky to net an additional two or three Senate seats. If the economy gets a head of steam, Democrats argue they can hold their own or even add a seat or two–though at the moment, that appears to be bravado.

It’s too early to say which party has the better prospectus for 2010, but it will be surprising if the GOP doesn’t make some progress in whittling down the large Democratic majority. And in the Senate, as we have all seen over the decades, movement of even a few seats in a party’s direction can change the outcome on the Senate floor for major legislation. A year in advance of a tumultuous midterm election, that possibility is the GOP’s realistic hope for 2010.