We continue to build make-shift monuments to victims of mass shootings.  It's the one thing we do well.  The most-recent case should teach us what we need to know.  There were many reason why this shooter should not have been allowed to have a gun.  And yet, all the warning signs were ignored.  When we refer to "common-sense measures," this what we reference.  I think most would agree that denying a person access to guns for the reasons enumerated in this case would be appropriate.  If you haven't been discharged, escaped from a mental hospital, threatened your mother-in-la or killed animals, there is no reason for you to be insecure about this issue.  On the other hand, if you disagree that there are certain valid reasons for denying someone access to guns, then you are contributing to the problem.