News arrived early this evening that Alan Khazei will announce tomorrow at noon that he is dropping out of the race for the Democratic nomination for US Senate in 2012. Khazei joins Setti Warren and Bob Massie as candidates for that office who have exited the race since Elizabeth Warren declared her candidacy. Besides Warren, others who remain in the race are Marisa DeFranco, Herb Robinson, Tom Conroy and James King.

While no one can count the remaining candidates out, the departure of Setti W, Massie and Khazei, three who prior to Elizabeth W’s entry into the race were seen to have good shots at winning, reinforces the perception that the Warren campaign is an unstoppable juggernaut in the Democratic primary, at least. If that is indeed the case, it’s debatable whether Warren would benefit more from having the others remain in the race or drop out entirely. In a contested race, she gains valuable experience in debates and is forced to guard against taking anything for granted. The upside of her running alone is that it would allow her to set her sights on Scott Brown right now and perhaps even engage him directly in debates in the coming months and not have to wait for the eight week window between the primary and the election to do so.