Gun control became a wedge issue with the 1968 Gun Control Act, the first piece of gun-control legislation passed since the 1930s. Following the assassinations of the Kennedy brothers and Martin Luther King Jr., as well as the urban riots of the 1960s, there was a widespread sense that greater government regulations on gun ownership were necessary. This led Lyndon B. Johnson to support a bill that prohibited interstate trade in firearms; denied gun sales to classes of people such as felons, minors, and the mentally ill; and prohibited the importation of military surplus weapons into the US.

Before this bill, the National Rifle Association had been somewhat accommodating toward gun control - its leaders had privately supported legislation vetted following the assassination of JFK - but during the public debate in 1968 the NRA began to use more aggressive techniques to lobby against the legislation.

One of the chief tools it used was the direct-mail campaign. What this meant was that the NRA would take the database of its several hundred thousand members and send them newsletters that framed the gun control issue in a way that emphasized the threats that it posed to their basic liberties as gun owners and citizens. The members, outraged by this information, would then write to their congressmen and ask them not to support the bill.

This technique had been pioneered by Richard Viguerie in the 1960s when he was with the conservative group Young Americans for Freedom, and was later used by a variety of other causes, from pro-life to right-to-work legislation. The genius of it was that it allowed groups by bypass the mainstream media and directly communicate to their constituents. The more alarmist the rhetoric used in these communications, the more active NRA members would be in speaking out against gun control legislation.

Although the NRA failed to defeat the 1968 bill, it became aware of its lobbying power while also learning techniques to influence public opinion. By the 1970s, it became more active as a lobby group - in contrast to the 1950s when it was essentially a sportingman's association in favor of gun safety. This transformation was complete by the 1977 NRA convention in Cincinnati, when hard-liners with an emphasis on grassroots organizing assumed control of the Association. At the same time, the NRA became more closely aligned with the Republican Party, and with a general neo-conservative revolt against the Great Society policies of the LBJ administration. The result was that gun control was transformed from a matter of public safety into a lightning rod in the culture wars of the 1980s and 1990s.

Sources: Osha Gray Davidson, Under Fire: The NRA and the Battle for Gun Control; Robert J. Spitzer, The Politics of Gun Control; Josh Sugarmann, National Rifle Association: Money, Firepower and Fear; Richard Viguerie, America’s Right Turn: How Conservatives Used New and Alternative Media to Take Over America; https://www.washingtonpost.com/politics/how-nras-true-believers-converted-a-marksmanship-group-into-a-mighty-gun-lobby/2013/01/12/51c62288-59b9-11e2-88d0-c4cf65c3ad15_story.html