What we are seeing with Cheney is emblematic of two trends on the issue. The first is that people that know gay people are almost twice as likely to support gay marriage. Actually knowing people in a group has a tendency to refute the prejudices about the group.
The second is the split between the public and private face of many politicians. I have heard for years that many Republicans would personally support gay marriage, and gay rights generally, but feel politically compelled to stay on the good side of the religious right. The candidates have to be careful what they say, but look at what people around them say and do. You see Laura Bush speak out against the Federal Marriage Amendment, John McCain’s campaign manager coming out for gay marriage, Bush’s solicitor general coming out for gay marriage, and so forth. Cheney is in a personal position that requires him to put the personal above the political. I believe that most national polticians, Rep and Dems, feel the same way, but they play the politics of the issue.
Dems are no better, they just have a different public face. They talk the rights game, but don’t do anything out of fear of backlash. Clinton talked a good game for years, but did little for gay rights when he was in office. We’ll see if Obam breaks ranks and actually does something to support equal rights for gay people, so far he is in the Clinton pattern, but its still early.