The issue of civilian gun ownership really started becoming a hot button political issue during the civil rights era of the 1960s. That’s not to say gun ownership was never brought up before that time, the nfa was passed in 1934 which essentially made it so if you had a sawed off shotgun or an automatic thompson you had to pay an additional fee and register it, but the idea of certain guns being permitted and certain people not being able to own a firearm came about at this time. As the 20th century moved along the firearms available went from revolvers and bolt action and lever action rifles at the turn of the century to automatic weapons, semi automatic rifles, and automatic pistols being readily available through surplus sales and the weapons arms companies would sell to governments also being available in their catalogues for the civilian market. This isn’t stuff like mortars and .50 cal machine guns per say(although they were legal) but stuff like Armalite selling the same automatic rifles to the government and civilians. The government started having issues with firearms like this during the civil unrest of the 1960s. The assassination of JFK with a mail order imported Carcano rifle from Italy and the killing of MLK were big contributors of it becoming an issue to bring up in the senate, but the biggest push for gun regulation was the arming of militant black organizations, primarily the Black Panther Party. Militant organizations like this would buy surplus military firearms and carry them around legally and use them to intimidate government employees and police, occasionally violence would result and often times police would be killed against them. This led to the gun control act of 1968 which banned importation of non sporting rifles (no more surplus firearms), felons could no longer own firearms, drug users could not (marijuana smokers included), all firearms registered with the US government, explosives were no longer legal, and all firearm sales had to be done through a federally licensed FFL. This was signed in by democrat president LBJ bur had a fair amount of support from Republicans and Democrats. But a lot of people took issue with the new gun control laws, especially civil rights organizations since so many of the new restrictions disarmed the black community. At this point is wasn’t necessarily Republicans or Democrats against the gun laws it was certain parts of society, your anti-government types (right wing militias, militant leftists, communes, etc). This stayed this way until the late 1980s and early 1990s when stricter and stricter gun control was being enacted to try and curb the spikes in gang violence happening around the country. Things like the Brady Bill were passed which mandated a 5 day waiting period and background check for any handgun purchase and increasingly strict requirements for carrying permits were a part of this new wave of gun control that the Republican party was opposed to and that was spearheaded by the Democratic party. This gun control was usually targeted at major urban centers but oftentimes expanded through whole counties or states. The rural Republican voter base that are being affected by these laws are the backbone of Republican opposition to gun control in the modern times.