Conversely, Democrats have three seats up in 2014 in states that Obama lost by more than 15 points: minus 17 points in Louisiana (Mary Landrieu), minus 24 in Arkansas (Mark Pryor), and minus 27 in West Virginia (Jay Rockefeller). It should be noted that six-term West Virginia GOP Rep. Shelley Moore Capito, announced her candidacy on Monday at the state capitol in Charleston.

In three more 2014 Democratic Senate states, Obama lost by at least five but less than 15 points: minus 11 in South Dakota (Tim Johnson) and minus 13 in both Alaska (Mark Begich) and Montana (Max Baucus). Former South Dakota Gov. Mike Rounds started an exploratory committee in September and is expected to challenge Johnson.

There are three more 2014 Democratic Senate seats up in swing states, defined as such due to 2012 margins of five points or less: Obama minus two in North Carolina (Kay Hagan), plus three in Virginia (Mark Warner), and plus five in Colorado (Mark Udall). That's nine Democratic seats that are either in demonstrably swing states or in enemy territory. This also does not take into account some states that were on the bubble: Obama won Iowa (Tom Harkin) and New Hampshire (Jeanne Shaheen) by just six points each.

The remarkable thing about Senate Democrats in 2012 was their ability to go on the offensive while, by necessity, playing defense. That will be much more difficult to replicate in 2014 given the seats up that cycle.

Republicans will still face the same obstacles they have had to contend with in the last two cycles: first, getting high-quality and electable candidates to run, and second, getting them through primaries. Their challenge, in part, is that too many traditionally Republican voters -- both of the moderate and the "mainstream" variety -- seem to have pulled back from active roles in GOP politics and even participation in primaries, allowing the more conservative wing of the party to become dominant. This has encouraged extreme candidates to run and has produced rather exotic and problematic candidates who often go on to lose general elections. Republicans took encouragement in Mitt Romney performing so well among independent voters, but the truth is that many of those were Republican-leaning independents -- voters who used to call themselves Republicans but have edged over one notch to the left -- who were uncomfortable with much of the rhetoric that has been projected in recent years.

But even if these candidates don't open their mouths, insert grenades, and pull pins (a la Todd Akin and Richard Mourdock), they still project a more extreme image for the party that makes it incredibly difficult for more-mainstream Republicans in swing or difficult states to win. For every Akin and Mourdock, there is a Scott Brown, a Linda Lingle, or a Heather Wilson who cannot win in tough places, at least in presidential years, because of the face of the Republican Party, a threatening brand to many moderate and swing voters.