I know, because with Senator Dianne Feinstein I led the effort to enact the 1994 law that banned assault weapons and high-capacity magazines for 10 years. Those gun safety reforms made our nation demonstrably more secure.

They were also, sadly, the last meaningful gun legislation we were able get signed into law before the N.R.A. and the gun manufacturers put the Republican Party in a headlock.

I fought hard to extend the assault weapons and high-capacity magazines bans in 2004. The Republicans who allowed these laws to expire asserted that they were ineffective. But, almost 15 years after the bans expired, with the unfortunate benefit of hindsight, we now know that they did make a difference.

Many police departments have reported an increase in criminals using assault weapons since 2004. And multiple analyses of the data around mass shootings provide evidence that, from 1994 to 2004, the years when assault weapons and high-capacity magazines were banned, there were fewer mass shootings — fewer deaths, fewer families needlessly destroyed.