1) Almost all gun related murders in the U.S. are committed via handguns not assault rifles. Most of these murders are also committed by people the victims knew and were generally related to domestic violence and drug related violence. President Obama can't do anything to address handguns due to the 2nd Amendment.
2) Even if assault rifles are banned (which I don't mind as long as it's okay with the 2nd Amendment), people can always get their hands on an assault rifle through the black market. People who have ill intentions with guns don't own registered weapons it would be foolish. So some sick individual who wants to commit mass murder could get his hands on about any weapon he'd like especially since he can use all the money he had as he wouldn't have any short or long-term financial needs. So a ban on assault rifles really won't do what everyone is hoping it would do. I'm not saying there aren't reasons to try and do it I just think that based on what we'd be trying to accomplish, it wouldn't work.
What upsets me most about all of this is how the Obama Administration went all out on this issue with the above points in mind. He did it for emotional reasons and probably political reasons as well because he is a politician after all. It is well known that a good economy reduces crime. Less than 100 people a year are killed by advanced weapons yet if he and his team would have been all hands on deck on the issues of debt reduction and over-spending he would have been addressing the needs of hundreds of millioins of people. Having managed people practically all my career and having been a business owner, I can tell you that prioritizing sometimes is a difficult task because everything seems critical but as a leader you know to focus on the controllables. You also have to prioritize clearly to your team what two or three issues are most critical so they don't go whichever way the wind blows everyday. It's tough for a leader because he or she has a tendency to want to fix everything but it's not realistic and if you spread your team to thin nothing will get done properly; basically a mile wide and an inch deep. I don't think President Obama showed good leadership on this one but I believe his heart was in the right place.