Ron Brownstein makes the smart point that Congressional Democrats have been much more willing to fall in line behind Obama and his legislative priorities this year than they were willing to support Bill Clinton's in 1993. The reasons, according to Brownstein: Obama scored a bigger electoral victory than Clinton; the great ideological "sorting out" that's occurred on Capitol Hill in the last 16 years, with conservative Southern Dems being replaced by non-Southern, suburban centrists; and a general decreased tolerance on the Hill for defections from the party line.
I think these are all right, but I also think Brownstein's selling Obama himself somewhat short. As far back as last summer, Obama's allies--especially those on the Hill--were talking about how Obama and his people had learned important lessons from Clinton's first term, in which the White House simply didn't do enough consulting with Congress. (Bill and Hillary's treatment of Moynihan on health care is only the most infamous.) The fact that Obama selected Rahm Emanuel as his chief of staff shows how committed he is to not making that same mistake. And I have to imagine there's been a lot of consultation (and coddling) to generate the impressive Congressional Democratic support he's received to this point.