While I don’t necessarily applaud Boxer’s motives, whatever they may be....I AM happy for her vote!
Her motive was the AFL-CIO’s opposition to the guest worker provisions of the Senate bill. You will note that the two dem. Senators from West Virginia also voted against cloture. The two deal breakers in the bill, even before the debate began, were the instant amnesty and guest worker portions of the legislation. Put another way, it puts blue collar workers (in both parties BTW) and Chamber of Commerce types against each other. The business types are the ones pushing for the amnesty part of the bill and were attempting to waterdown the enforcement measures in the bill. However, a group of conservative Pubbies would not let them do that since they realize the public in general prefers tougher measures in that regard.
Underlying all these shanigans is the tendency of Senators to avoid tough, contentious votes, thus the need to dream up ineffective compromises to protect their backsides in the next elections, individually and collectively as political parties.