In his weekly conference call with reporters, Portman was pressed on his vote in 2013 against the Manchin-Toomey Amendment, which would have required background checks for weapons bought at gun shows or on the Internet. He was vague in recalling his overall objections, but said he felt the amendment may have reached too far.

“I think their notion was to try to deal with gun shows as I recall. And in gun shows, it’s primarily licensed dealers and they should all be subject to background checks and I agree with that. (But) I think they were expanding it in ways that, would affect let’s say a family, passing down a weapons, a shotgun, say, from a father to a son.”

Investigators have said all four guns used by Syed Rizwan Farook and his wife Tashfeen Malik  in the San Bernardino attack were purchased legally four years ago. California requires paperwork when a gun is transferred, but other states do not.

Portman maintains this mass killing appears to differ from those spawned by mental illness.

“I’m not saying that there shouldn’t be again better enforcement and there should certainly be much better mental health records and other things we talked about in terms of these other mass shootings. In this case, I just don’t know enough about what happened.”

But other cases, he maintains, may have been avoided with better sharing of mental health, criminal and criminal background information.