Several Democratic presidential hopefuls took to Twitter on Saturday to commemorate the 20-year anniversary of the Columbine High School shooting in Littleton, Colorado.

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"Twenty years ago, when I was 17, the shootings at Columbine broke America’s heart. Today’s high schoolers have seen the same kind of horror at Parkland and elsewhere. If we don’t want to repeat this in 20 years, we must summon the courage to deliver common-sense gun reform," Buttigieg wrote in a tweet Saturday.

Twenty years ago, when I was 17, the shootings at Columbine broke America’s heart. Today’s high schoolers have seen the same kind of horror at Parkland and elsewhere. If we don’t want to repeat this in 20 years, we must summon the courage to deliver common-sense gun reform. — Pete Buttigieg (@PeteButtigieg) April 20, 2019

"Twenty years later, our hearts are still with the # Columbine community. Now, as mass shootings have become an almost-everyday occurrence in America, we cannot lose our sense of outrage. We must stand up to the NRA and end our gun violence epidemic," Sanders said.

Twenty years later, our hearts are still with the #Columbine community. Now, as mass shootings have become an almost-everyday occurrence in America, we cannot lose our sense of outrage. We must stand up to the NRA and end our gun violence epidemic. — Bernie Sanders (@BernieSanders) April 20, 2019

“Remembering the 13 killed and 24 wounded in the tragic shooting at Columbine High School. Twenty years have passed, but we haven’t made twenty years of progress on gun violence prevention. It’s time to pass gun safety legislation,” Klobuchar tweeted.

Remembering the 13 killed and 24 wounded in the tragic shooting at Columbine High School. Twenty years have passed, but we haven’t made twenty years of progress on gun violence prevention. It’s time to pass gun safety legislation.https://t.co/NZNMJm3Oqv — Amy Klobuchar (@amyklobuchar) April 20, 2019

“Twenty years after Columbine, the survivors are now confronted with how to tell their children about it — when their own kids are participating in school lockdown drills. The entire Littleton Community is in my thoughts today,” Harris tweeted.

Twenty years after Columbine, the survivors are now confronted with how to tell their children about it — when their own kids are participating in school lockdown drills. The entire Littleton Community is in my thoughts today.https://t.co/snxUQFlDWI — Kamala Harris (@KamalaHarris) April 20, 2019

"20 yrs later, we remember the #Columbine victims. Sadly, it hasn’t become harder for the most dangerous people to get the most dangerous weapons. It’s become easier. We can protect our kids in their classrooms with: ✅Background Checks ✅Assault weapons ban ✅Anti-gang programs," Swalwell, who has made gun control the centerpiece of his presidential campaign, said.

20 yrs later, we remember the #Columbine victims. Sadly, it hasn’t become harder for the most dangerous people to get the most dangerous weapons. It’s become easier. We can protect our kids in their classrooms with:

✅Background Checks

✅Assault weapons ban

✅Anti-gang programs — Eric Swalwell (@ericswalwell) April 20, 2019

“On today's 20th anniversary of the shooting at Columbine High School, we must remember that thoughts and prayers aren't nearly enough. Our students and our families deserve nothing less than a nationwide effort to reduce gun violence and take weapons of war off our streets,” Inslee said.

On today's 20th anniversary of the shooting at Columbine High School, we must remember that thoughts and prayers aren't nearly enough. Our students and our families deserve nothing less than a nationwide effort to reduce gun violence and take weapons of war off our streets. — Jay Inslee (@JayInslee) April 20, 2019

"A lot can change in 20 years. It should change. We shouldn’t know the words Sandy Hook, Tree of Life, Mother Emanuel, Pulse, or Parkland—not for the reasons we do. Yet there they are, part of our shared vocabulary of frustration and grief," Hickenlooper said in a press release, citing the sites of other shootings.

"In our state and across our country, we can and must do more. We can raise the required age for gun purchases; we can pass red flag laws," he continued. "That spirit of action that moved us in Colorado needs to become the norm in Washington. We can’t look back again, another 20 years from now, having allowed countless more names—of schools, places of worship, or public spaces — to become part of our lexicon of grief."

Gun control has become a hot button issue for the Democratic Party after a recent string of high-profile mass shootings, including last year’s shooting at Parkland, Fla.'s Marjory Stoneman Douglas High School that killed 17 people. The shooting reignited the debate surrounding gun control legislation and sparked the March for Our Lives movement, which advocates for stricter gun control measures.

Democratic 2020 candidates have embraced gun legislation as a focal point of their campaign platforms. House Democrats, meanwhile, passed two gun bills earlier this year.

Updated at 4:12 p.m.