The tie between gun control and lower crime rates has never been clearly established. Proponents often rely on cherry-picked anecdotal evidence that ignores many variables and contrary evidence, these are not scientific methods by any means. Many states and cities with strict gun control measures lead the nation in violent crimes. The CDC could find no link between gun control and lower crime rates, why not have them do another study? Compare TOTAL crime rate, violent crime and murders before and after gun control measures like those you seek to enact. Make your case based on more than emotion.
If the president is interested in representing all people, as he suggests, he will not ignore the concerns of law abiding gun owners, nor exploit the recent tragedy for political points.