Jonathan Chait notes that Republicans aren't using the filibuster to block the immigration reform bill in the Senate and speculates that the lack of procedural resistance bodes well for eventual passage.
It’s a vote to have a debate on immigration reform, not a vote for a particular bill, which is sure to attract fewer than 82 votes in the end, and probably far fewer. But it gives the general impression that conservative opponents are merely going through the motions and have made their peace with a likely defeat. And that impression is not wrong.
That 82 votes is a signal that Republicans in the Senate are, indeed, not using every tool they have to block a bill. Eighty-two votes to proceed is a way of signaling that the status quo, not the expected outlines of a bill, is what is most unacceptable. This is the opposite of how Republicans have approached the major legislation of the Obama era, beginning with the stimulus, when they did not make any distinction between voting to allow debate and voting on the underlying merits of the final bill. Republican senators today faced a choice to position themselves as fundamentally opposed to the entire process, and most of them decided to stand aside.
Would Sen. Mark Pryor have preferred a filibuster so it never made it to the Senate floor? Maybe that's too cynical, but given the political dynamic in Arkansas, Pryor may be squeamish about delivering a needed vote. Jordan Fabian at ABC News cites him as one of four Democratic Senators that might vote no. Pryor voted against the immigration reform bill in 2007. He has said that immigration reform is needed but has been noncommittal thus far about the Gang of Eight bill. He predicted in the Wall Street Journal last month that a bipartisan bill would eventually pass the Senate and seemed to hint that he was hoping for cover, telling them that ideally the bill should gain broad enough support to get "north of 70 votes."
What happens if, as in 2007, there's a popular backlash among conservatives? Well, passing a bill may be dependent on the political bravery of Mark Pryor.