Sen. Tom Coburn (R-Okla.) effectively squashed an amendment to the defense authorization bill Thursday that would have enhanced retirement benefits for federal employees.Coburn, a staunch fiscal hawk, filibustered the measure for 90 minutes on the Senate floor, arguing that the amendment was not germane to the bill. It was eventually withdrawn by its sponsor, Sen. Daniel Akaka (D-Hawaii).A major backlog of amendments to the defense bill remains, however, and Democratic and Republicans leaders continue working to reach an agreement for final passage. If no agreement can be reached, the Senate is poised to vote on Friday on a motion to move to final passage.