The Wall Street Journal had this to say:
A word, first, about that Senate "minority." Majority Leader Harry Reid was free to bring the deal struck by West Virginia Democrat Joe Manchin and Pennsylvania Republican Pat Toomey to the floor for an up-or-down vote, and this background-checks amendment might have passed. It did convince 54 Senators, including four Republicans.
But under Senate rules, a simple majority vote would have opened the measure to up to 30 hours of debate, which would have meant inspecting the details. The White House demanded, and Mr. Reid agreed, that Congress should try to pass the amendment without such a debate.
Majority rules would have also opened the bill to pro-gun amendments that were likely to pass. That would have boxed Mr. Reid into the embarrassing spectacle of having to later scotch a final bill because it also contained provisions that the White House loathes. So Mr. Reid moved under "unanimous consent" to allow nine amendments, each with a 60-vote threshold.
The White House was right to worry. An amendment from John Cornyn of Texas that would have required all states to recognize every other state's concealed-carry permits earned 57 votes, 13 Democrats among them. The nearby table has the list. On Thursday, Wyoming's John Barrasso offered an amendment to protect gun ownership privacy that passed 67-30.