In 2004, a federal ban on assault weapons expired. Republicans refused to support it. Mass shootings have since tripled. 3500 mass shootings. The Second Amendment is not a suicide pact.
Zusha Elinson is writing a history of the AR-15 military style weapon used in most mass shootings. He notes that there were about 400,000 AR-15 style rifles in America before the assault weapons ban went into effect in 1994. Today, there are 20 million.
In 2008, in the infamous Heller decision, the Supreme Court said for the first time that individuals have a constitutional right to own firearms outside of membership in a militia or for traditional purposes such as hunting or self-defense. This limited the ability to enforce gun safety laws.