A bi-partisan proposal to mandate an expanded use of background checks on gun buys is considered in jeopardy in the U.S. Senate due to dwindling Republican support. Iowa Senator Chuck Grassley, the ranking Republican on the Senate Judiciary Committee, says he won’t back the measure.

Grassley says, “Since we had testimony before our committee from the Institute of Justice that (for) background checks to be effective you’re going to have to have registration with them, and since I don’t want gun registration because I don’t want the government to know where all the guns are, I’m going to vote against this provision.”

The legislation would require background checks be done on all gun sales at venues like gun shows and online. Background checks are only required now on sales through federally-licensed gun dealers. Some opponents of the proposal say it would violate the right to bear arms that’s guaranteed in the Constitution.

Grassley says, “I expect the main reason this provision will lose is because compromising any of our Bill of Rights, whether it’s the First Amendment, the Second Amendment, the Fourth Amendment, the Fifth Amendment and you know how important all those are, people consider it a slippery slope and don’t want to go down that slippery slope.”

Monday’s bombings at the Boston Marathon killed three people and injured more than 140, but Grassley doesn’t expect the violence will have an impact on the looming vote to more closely regulate guns. “I don’t think yesterday’s killing in Boston is going to have anything to do with it,” Grassley says.

“That could be an international plot within the United States. We don’t know yet for sure, but it could be. The FBI is investigating that.” Earlier, Grassley made a statement: “Our thoughts and prayers are with the people of Boston and the people who are suffering and the families of those who were killed.”

Radio Iowa