So if the Democrats lose the senate.

[Jim Lane]

65. Legislation is already irrelevant. The issue is nominations.

The Senate will be close, but it won't matter for legislation. Anything notably good will die in the House. Anything notably bad will be vetoed. The Senate composition might have some marginal influence on legislative compromises made to keep the wheels turning, but that's it.

The real question about a Republican-controlled Senate is what they'd do about nominations. We could see many unfilled positions in the executive branch and many many unfilled judicial vacancies.

As to the OP's question about the blame game, it might be that the single most important question is the blame game as it affects Republicans. If they get a Senate majority and use it for full-on obstructionism, it might hurt them at the polls in 2016. If the party elders try to rein in the Tea Party hotheads and go for less than full-on obstructionism, it will exacerbate the existing internal rift.

On the Democratic side, I don't see the left getting the blame (at least from anyone whose opinion matters). The Republican path to Senate control is chiefly through beating conservative Democrats like Landrieu, Pryor, and Hagan. The progressives like Ed Markey are not in serious danger. A good year for the Republicans will mean that the center of gravity of the diminished Democratic caucus will shift to the left.