The NRA is very strongly involved in US politics. It lobbies very vigorously and spends money to try to influence members of Congress to vote in ways that the NRA would like on the subject of gun control.
The NRA is seen as one of the most powerful lobbying groups in Washington. This is largely because of its large membership and (more importantly) the fact that its membership is very united and very passionate about resisting any laws that would regulate the right to bear arms.
As an example of this, the NRA was successful in 2004 in getting Congress to allow a ban on semi-automatic weapons to expire.