I might as well make my predictions and set myself up for ridicule and humiliation. The short version is that I think the Democrats will loose at least six seats, but hang on to a narrow majority in the Senate. I haven't watched enough individual races to predict a number, but my sense is that the Republicans will carve out a narrow majority. The result will be total gridlock, two years of burnt-earth tactics by the Republicans that will make this year look like the very model of collegiality, too much grandstanding by Joe Lieberman, and even more noise from the Tea Party (though not necessarily under that name).
First the Senate. Thirty-seven seats are holding elections; sixty-three are not. Of the seats not up for election, thirty-eight are Democrats, two are independents who caucus with the Democrats, and twenty-three are Republicans. Nineteen Democratic seats are up for election and eighteen Republican. Normally, that would look good for the Democrats, but this isn't a normal year.
The Democrats will definitely loose two seats (Arkansas and North Dakota). There are four Republican seats where Democrats have a chance (Alaska, Kentucky, Missouri, and New Hampshire), but these are all fairly conservative states, so I'm not counting on any of them. The remaining fourteen Republican seats are all safe for them to keep. Of the remaining seventeen Democratic seats, I'll call seven safe (Delaware, Hawaii, Maryland, two in New York, Oregon, and Vermont). That means the best the Democrats can hope for is to see their majority from drop fifty-nine to fifty-seven.
What about the other ten Democratic seats? There are four that I'd say look good for Democrats (California, Connecticut, Washington, and West Virginia), though all are closer that they should be. Two look good for the Republicans (Wisconsin and Indiana). At this point, we have a Senate of forty-five Republicans, forty-nine Democrats, two independents who caucus with the Democrats, and four seats that are toss-ups (Colorado, Illinois, Nevada, and Pennsylvania). Nate Silver, who had the best record for calling races in the last election, gives the Republicans the advantage in all four races but things are pretty volatile right now. For the moment, I'll split the difference on those and say the Democrats rally enough to save two of those seats, probably Illinois and Nevada.
The House is pretty obscure to me. I can only speak in vague generalities. There are 435 seats in the House. Democrats currently hold 255, Republicans 178, and two are vacant. All of them are up for election. It takes at least 218 to make a majority. That means the Republicans need to gain exactly forty seats to gain a majority. Most pollsters say the Republicans will gain a narrow majority. The question is, how narrow? Today I'll say very narrow, no more than ten seats.
Both parties are working on their get out the vote (GOTV) efforts. In addition, Republicans have some pretty aggressive voter intimidation efforts going in a few states. Some states will drag out the decision for weeks after the election and some will result in lawsuits (Alaska will have both). It's cliche to say that turnout is what really decides the election, but this year that's more true than usual. The far right is very mobilized and the left is very discouraged. I see three wild cards in polling and turnout.
First, cell phones have made polling less dependable than it sued to be. Polling under-represents cell phone users who tend to be minorities and well wired white folk. Both of those groups lean Democratic. Pollsters try to correct for such things, but their corrections are just guesses. Nate Silver doesn't actually poll; he interprets other people's polls so his predictions will depend on how well the pollsters make their corrections. Second, while the Tea Partiers are motivated as all git out, many of them have previously been non-voters. I haven't seen any information on whether their enthusiasm has been converted into a wave of new voter registration. Third, the "unmotivated" left is very scared by the Tea Party. All of the polling has assumed that we will not vote. That could change over the last few days before the election.
The the short version is this: Democrats will keep a thin majority in the Senate and Republicans will gain a thin majority in House.
Next: what comes after the election.