Peggy Noonan on the Democrats and Abortion.
I think she has this part of the issue nailed:
The Democratic Party, in contrast, has exhausted its great reasons for being, having achieved so many of them during the past 75 years. The Democrats often seem like the Not Republican Party, no more and no less. It is composed not of allied groups in pursuit of the same general principles but warring groups vying for money, power, a louder voice, the elevation of their particular cause.
The one thing they agree on, that holds them together and finances their elections, is abortion. The abortion-rights movement packs huge clout in the party; it can make or break a candidacy with contributions and labor and support. It has such clout that at the 1992 Democratic convention the party wouldn't even let Gov. Bob Casey of Pennsylvania, a popular liberal from a state with 23 electoral votes, give an afternoon speech. He was officially a nonperson at his party's convention because he was pro-life. The Republicans, on the other hand, still have arguments over abortion. Whether pro- or anti-, it is understood you are not banned from a convention podium on that basis. The Republicans can still have a conversation, albeit with occasionally loud voices. But better a loud voice than no voice at all.
[Link via Amy Welborn.]