The columbine is a perennial flower often seen growing wild in the Rocky Mountains. But since April 20, 1999, the word has been a universally recognized reference to what was then the worst mass shooting at a school in American history. Thirteen people were shot to death and 21 were wounded by a pair of Columbine High School students who then killed themselves. The massacre in Littleton, Colo., was a singularly shocking event.

At the time, the bloodshed seemed as though it might create a turning point in public attitudes and government policy on firearms. President Bill Clinton proposed measures to regulate sales at gun shows, raise the minimum age for buying handguns from 18 to 21 and hold negligent parents liable if their kids commit crimes with firearms. Texas Gov. George W. Bush endorsed instant background checks at gun shows.

The Republican-controlled U.S. Senate voted against this safeguard just weeks later — and immediately reversed course, fearing how voters would react.

As it happened, things didn’t change as much as some expected. In 2000, 70% of Colorado voters supported a ballot initiative closing the “gun show loophole.” But Clinton had no luck on his legislation. Al Gore’s narrow defeat by Bush in the 2000 presidential race was blamed partly on his support for gun restrictions. As president, Bush not only didn’t push for broader background checks, he also let the 1994 federal assault weapons ban expire.

School shootings may still cause horror among Americans, but they provoke more shock than surprise. Columbine is no longer the most deadly, having been surpassed by the massacres in Newtown, Conn. (2012), and Parkland, Fla. (2018).

Over these two decades, the Supreme Court also has expanded the rights of gun owners in decisions on the Second Amendment. All states now allow the carrying of handguns in public under some conditions — reflecting a judgment that armed, law-abiding citizens can deter armed criminals.

Twenty years on, though, the 1999 shootings can be seen as the beginning of a gradual shift in public sentiment. A 2018 Gallup Poll found that 92% of Americans favor requiring background checks for all purchases. In February, the House passed a bill mandating that change — indicating that Democratic politicians no longer fear the wrath of the National Rifle Association.

In the aftermath of Columbine, Americans began searching for ways to protect kids from being riddled with bullets as they attend school. Twenty years later, the answers still elude us.