Dan Freedman of the Times Union in Albany, N.Y., provides a great explainer on the history of the background-check debate that reaches back to 1986. Congress passed the Firearms Owners Protection Act that year, which banned the production and possession of most fully automatic machine guns. The act didn't make many headlines, "but in retrospect, this innocuous-sounding piece of legislation contained the seeds that sprouted into the debate over expanded background checks underway yet again on Capitol Hill in the aftermath of mass shootings in Ohio and Texas," Freedman reports.
That's because the FOPA Act specified which gun sellers needed a federal firearms license and which didn't. Gun owners who buy, sell, or exchange firearms only occasionally for a hobby or personal collection do not need a license. The National Rifle Association and the act's supporters in Congress (many Democrats from pro-gun rural districts) counted this as a major win, Freedman reports. With the legal blessing of the FOPA Act, gun shows became more popular.
Gun shows became even more popular after the Brady Handgun Violence Prevention Act passed in 1993. It mandated background checks for anyone who bought a firearm from a federally licensed dealer, but preserved the gun-show loophole. That encouraged more people to buy and sell at gun shows or online. Background checks are required for online sales across state lines, but not if the sale is within a state that doesn't require background checks as a matter of state law. Only 12 states require background checks on all sales, including private ones, Freedman reports.