Coakley is apparently not the only Democrat nervous that she will lose. If Brown takes the seat the Democrats filibuster proof majority disappears instantly. All the massive programs they are pushing through now (think healthcare overhaul) can not spare a single vote and still may not pass. Some Republicans and conservatives are concerned that if Brown wins the Democrats may purposely delay seating him. Barney Frank (D) thinks that concern is 'the stupidest thing he has heard in a long time'. They may not have to. The Democrats new tactic appears to be pushing through the compromise and vote before the election. They only have a few days to work it out and risk a collapse of the fragile compromise between their own party. This seems a pretty clear indication that they see at least a decent chance of Brown being elected.
Past related post:
Berman Post: Scott Brown vs Martha Coakley For Massachusetts Senate
Berman Post: Coakley Getting Nervous