The creation of laws is an extremely grave responsibility, especially when the laws impact Constitutionally protected rights.  Laws must be extremely well thought out with maximum benefit and minimum harms.  To knee-jerk another layer to background checks - violations of which the President is choosing not to prosecute - will do no good - will have no effect on crime.  Banning assault weapons will also have no effect, it's already been proven.  Why put a law into place that you know will have no positive effect?