Yeats wasn't talking about Blue Dog Democrats when he wrote "The Second Coming," but one line of that masterpiece seems appropriate to the political situation today: "Things fall apart; the centre cannot hold."
Political looks at the difficult elections prospects of a host of moderate-to-conservative Democrats in the 2012 election, a development on the left that is as troubling as the retirement of moderate Sen. Olympia Snowe is for the right. Moderation is not a value per se, but it is necessary in a democracy to have politicians within each political party that are willing to challenge the orthodoxies of their own. Only a pro-life Democrat can ever hope to bring the rest of that party to a reconsideration of their views, just as only a pro-immigration reform Republican can get her party to reconsider their views on that issue.
Unfortunately, the increasing dependence of members of Congress on the mopre extreme elements within their parties is a problem for which no solution seems plausible. As long as redistricting is done along partisan lines, all the political juice will come from the extremes.