In principle, 2014 looks like a very good year for Senate Republicans. They have only 14 seats up for releection to the Democrats' 21, and 13 of the 14 Republican-held seats are in deep red states. In contrast, the Democrats have to defend incumbents in states like Alaska, Arkansas, Louisiana, and North Carolina. The Democrats are also defending open seats in Iowa, South Dakota, and West Virginia, which, although not lost causes, are at least competitive.
The Democrats' fundamental problem is that weak Democrats rode to victory in 2008--a Democratic wave year--on President Obama's coattails. That option is not available in 2014, so many of these Democrats are going to have to fight for their political lives. If the Republicans can pick up five seats, the current 55-45 Democratic majority will vanish and Vice President Joe Biden will get a day job as President of the Senate. If the Republicans can pick off six seats, Sen. Mitch McConnell (R-KY) will become majority leader.
So far, the picture looks pretty rosy for the Republicans, but there's a catch. In 2012, many observers expected the Democrats to lose their 53-47 majority in the Senate because they had to defend 23 seats to the Republicans 10. It didn't happen. The Democrats ended up with a gain of two seats, largely because the Republicans fielded poor candidates. That could happen again in 2014. A battle is brewing already, basically about whether the Republicans want to nominate moderates, who can win the general election, but who are regarded as RINOs by the tea party, or extremely conservative candidates who can win the Republican primary but not the general election.
Two cases in point. In West Virginia, Rep. Shelley Moore Capito (R-WV), daughter of former governor and felon Arch Moore, is running for the seat being vacated by Sen. Jay Rockefeller (D-WV). She is a moderate and could probably win. However, the Club for Growth is looking for someone to run against her in the Republican primary. Similarly, popular former governor Mike Rounds (R) is running for the seat being vacated by Sen. Tim Johnson (D-SD), but former senator Jim DeMint, now head of the conservative Heritage Foundation, doesn't think he is conservative enough and is looking for someone to take him on in a primary.
However, the establishment is fighting back. Karl Rove, has created a Conservative Victory Project expressly for the purpose of helping candidates the Club for Growth, DeMint, and other very conservative outside groups oppose. This could lead to fireworks, as high-profile, well-funded, Republican groups duke it out. The Washington Post has a good article today about the coming fratricide. For a run down of all 2014 Senate races, click on the "Senate candidates" link in the blue bar at the top of this page.