Speaking as a liberal, when are we going to grow some balls and stop running scared? The right - both the cultural right and the corporate right - has been defining the terms of the game so well for so long that we're scared of our own shadows.
We also love the circular firing squad. I've seen people threaten to vote third party in 2012 on the left because of [insert failure of the Obama campaign/admin here] since the end of the primaries. I've seen people threaten to withhold time and money from the national party because we left Max Baucus stay in, or didn't fight hard enough for Franken, or didn't immediately push for single-payer, or didn't let Kucinich win the primary. Our House Speaker, supposedly our party's leader in Congress, is being challenged in a primary. We love to make things easy for our opponents.