While most of the attention for the next six months is going to be focused on the Presidential race, there are also Congressional elections to worry about, and the possibility that a major shift in party control could take place regardless of what happens in the Presidential race. On the House side, notwithstanding Democratic dreams, it seems rather unlikely that the Republicans will lose control of the body. Thanks in large part to the fact that a large number of the Republican victories in 2010 were in Districts that have been trending red for years, as well as the fact that redistricting has been very beneficial to the GOP in a number of states over the past two years, the most likely outcome is that the Democrats pick up a few seats but nowhere near enough to regain control. In the Senate, though, things are far different. Right now, that body is divided 53-47 in favor of the Democrats, and at this point it’s fairly clear that anything could happen in November:

Republicans need to pick up four more seats to take control of the Senate, and a year ago they had many plans for how to do so — none of which envisioned a battle to hold on to Indiana.

But Tuesday’s landslide victory in the GOP primary by Indiana state Treasurer Richard Mourdock, a staunch conservative who beat longtime Sen. Richard G. Lugar, gave Democrats hope for claiming a seat they have not seriously contested in three decades.

The sudden opening reflects a growing sense that the potential for big Republican gains has begun to ebb and that Democrats have a real chance of hanging on to their majority.

“Eight months ago, I thought that Republicans had a 60 to 65 percent chance of taking the majority. Now, it’s a 50-50 proposition as to whether Republicans can take the majority,” said Jennifer Duffy, a longtime expert on Senate races who works for the independent Cook Political Report.

Stuart Rothenberg, editor of the Rothenberg Political Report, said he places his “pinkie on the scale” now for Democrats retaining the majority, but added that his calculation hinges on economic improvements, particularly as reflected in the monthly unemployment numbers. “A few more months of less than 200,000 new jobs, and I take my pinkie off that scale,” Rothenberg said.

If Mourdock — a longtime politician twice elected to statewide office — can unify Republicans, he should be a favorite in GOP-leaning Indiana. But if his candidacy gets swept up in the fervor of the tea party movement, as some 2010 Republican nominees did, then Indiana could turn into a headache for national Republicans who would prefer not to expend resources to defend that seat.

“Lugar’s loss in Indiana put the seat in play, but only marginally improved Democrats’ chances of picking it up,” Duffy said.

But it was not supposed to come down to this: Republicans gained six Democratic seats in the 2010 midterm elections and, early on, 2012 looked to be even easier, with 23 Democrats up for reelection, compared with 10 Republicans. The Democratic president was deeply unpopular, and six Democratic incumbents and one independent, who generally votes with them, announced plans to retire. Those departures gave Republicans seven open-seat targets to pick from.

Democratic retirements in solidly red Nebraska (Ben Nelson) and North Dakota (Kent Conrad) seemed like sure GOP pickups, while vulnerable incumbents in Missouri and Montana, both of which Obama lost in 2008, seemed to be laying the groundwork for a GOP majority.

Originally, strategists and analysts predicted that this scenario would decide the majority: GOP gains in Missouri, Nebraska and North Dakota would push Republicans to 50 seats, and a victory in either Montana or Virginia would seal the elevation of Minority Leader Mitch McConnell (Ky.) to majority leader.

Republicans still appear to be in fairly good shape in Nebraska, even though Democrats recruited former senator Bob Kerrey to run. In Missouri, Sen. Claire McCaskill, who won with 50 percent of the vote in 2006, remains in a difficult spot, as polls show her in the low 40s, but Democrats say that the lackluster field of challengers in the August primary gives her a potential opening for victory. In North Dakota, Democrats have recruited former attorney general Heidi Heitkamp to face the winner of a June 12 GOP primary between Rep. Rick Berg and 2000 Senate nominee Duane Sand.

But the professional handicappers say that although they still expect GOP gains, Democrats are slightly favored to retain their majority, and the majority party is likely to hold just 51 seats — or 50, with the vice president serving as the tiebreaker.

As I said the other day, I think it at best premature to say that Indiana is a possible Democratic pickup merely because Lugar lost and Mourdock won. Mourdock has won statewide elections in Indiana twice in the last six years, most recently by an overwhelming margin. More importantly, though, it seems highly unlikely that the Hoosier State will go Democratic this year in the Presidential election. That fact alone is likely to help Mourdock in the General Election. Now, it’s certainly possible that Mourdock will mess up on the campaign trial between now and November and  the assessment will change, but until that happens I would keep Indiana’s Senate seat red for now.

That isn’t necessarily true for other states. Most importantly, the likelihood of Republican pickups in states like Missouri, Virginia, Florida, and Wisconsin seems far less certain than it was several months ago. Of those four states, the most likely pickups would seem to be in Virginia, where former Governor George Allen and former Governor Tim Kaine are essentially tied in the polls right now, and Wisconsin where former Governor Tommy Thompson seems to have a solid chance of both winning the GOP nomination and winning the General Election. The other two states, Missouri and Florida, are far more tenuous. The potential opponents to Claire McCaskill seem especially weak, and Florida Senator Bill Nelson continues to lead all potential GOP opponents in the polls.

The states where GOP pickups seem most like are those — North Dakota, Montana, and Nebraska — that have been trending Republican for years now.

The bigger problem for the GOP, though, is the possibility that its efforts to gain control of the Senate could be hindered by losing seats currently held by Republicans. Massachusetts is the obvious example, of course, even though Scott Brown continues to perform surprisingly strongly in the polls against Elizabeth Warren. Just north of Brown’s territory, though, it now seems pretty obvious that the GOP will lose the seat being vacated by Olympia Snowe. At the moment, polling shows former Governor Angus King, an Independent, leads potential Republican and Democratic opponents by a wide margin. King has not said which party he would caucus with if he wins the election, but it’s widely thought that he would end up with the Democrats, or at least that he would end up caucusing with whichever party has the majority to begin with. Of course, there’s the interesting possibility that King himself could end up being the person who decides which Caucus has the majority.

After running a few scenarios over at 270ToWin.com, here’s what I came up with:

• The most optimistic outcome for Republicans would include winning MO, FL, VA, and WI, picking up NE, ND, and MT, holding on to MA, and convincing Senator-Elect King to caucus with the GOP, that would give them a 54-46 majority.
• The most optimistic outcome for Democrats would include winning MO, FL, VA, and WI, holding on to NE, ND, and MT, picking up MA, and convincing Senator-Elect King to caucus with them. That would give them a 55-45 majority. Given them IN, and it increases to 56-46
• There are two quite likely scenarios that would lead to a 50-50 tie. Under one, the GOP picks up NE, ND,  MO, and MT and holds on to MA. Under another, you replace MO with VA and get the same result. In that case, tie votes (including leadership votes) are broken by the Vice-President, who will be Joe Biden until at least January 20, 2013.
• Right now, I would say the most likely scenario is either one of the 50-50 outcomes underlined above or a 51-49 split in favor of the Democrats resulting from Democratic wins in Missouri and Virginia.

The one thing you’ll notice from all of these scenarios is that, regardless of which party wins the Senate in November, they will do so with the thinnest of majorities. The Supermajority that the Democrats won in 2008 is long gone, and not likely to return any time soon. More importantly, regardless of who becomes Majority and Minority Leader in 2013 they are going to have to find a way to work with the other side, otherwise the Senate is going to become even more dysfunctional than it already is.