The U.S. Senate rejected Wednesday an amendment aimed at strengthening laws on background checks to purchase firearms, the Christian Post reports. The 54-to-46 vote fell six votes short of the 60 needed to advance the amendment. Drafted by Sens. Joe Manchin (D-W.V.) and Pat Toomey (R-Pa.), proponents of the amendment had hoped for bipartisan support, but support for the law unraveled under intense lobbying from gun rights groups. The NRA threatened to defeat senators who voted for it in their next election, arguing it would criminalize private transfers of firearms between law-abiding citizens. President Barack Obama had called for a number of other new gun control measures, including a ban on assault weapons and limiting the size of gun clips, but these other proposals were dropped for lack of support.