This is simple.
Obama got caught red handed in Fast and Furiuos trying to gin up fear and motivation for gun control so rather than risk losing his re-election bid he declared executive privilege and refused to turn over documents that would prove his involvement. He also avoided any mention of gun control for the same reason.
Now that he's been re-elected he is exploiting the first gun violence incident to push the agenda he's kept hidden for the past 4 years.
Welcome to the Fundamental Transformation of America.