What's driving the public chatter over gun control? I'm surprised to say it's probably the White House (emphasis mine):

What’s interesting about this is that it provides at least some rudimentary evidence that it is not just those in the media that are continuing to talk about topics such as gun control; it is the mass public as well. That being said, the biggest boost in the discussion of the issue by the mass public (the second set of peaks on the right part of the figures) came following President Obama’s gun control speech on January 16th, suggesting that while the public remains interested, elites (and especially the president) can play an important role in sustaining that interest. Of course, the data (which show tweets on “gun control” trending up before the President’s speech) are also consistent with a world in which public opinion may have encouraged him to act as well. ...

[T]he pattern of Tweets clearly is consistent with Danny’s claim that the Tweeting is being driven by the White House as opposed to visa versa. And yet, it is still interesting to see that it is not just journalists “covering the story”, but indeed tens if not hundreds of thousands of individuals (with the caveat again that these are just counts of tweets) that are doing so as well. The ability to see citizens in action this way is a new opportunity for social scientists—as indeed is the ability for citizens to “speak” publicly in this way!—and one which I think will prove very interesting to follow.