President Donald Trump and Colorado Gov. John Hickenlooper ordered flags flown at half-staff Thursday through sunset Monday in honor of the victims of Wednesday's shooting at Marjory Stoneman Douglas High School in Parkland, Fla.
Seventeen were killed and 14 wounded in the attack, allegedly perpetrated by Nikolas Cruz, an orphaned 19-year-old with a troubled past and an AR-15 rifle. Cruz was charged with 17 counts of premeditated murder Thursday morning.
"Colorado knows Florida's grief all too well, and we stand with them tonight," Hickenlooper tweeted just before 10 p.m. Wednesday. "We offer our support and heartfelt condolences."
There were "so many signs" Cruz was "mentally disturbed," Trump tweeted Thursday. "Neighbors and classmates knew he was a big problem. Must always report such instances to authorities, again and again!" he added.
Most members of Colorado's U.S. congressional delegation toed party lines when responding to the massacre, with Democrats generally calling for gun control and Republicans limiting their responses to condolences.
"I'm deeply saddened, but I'm also angry that we cannot pass ANY common sense gun violence prevention measures in the US Congress," U.S. Rep. Ed Perlmutter, a Democrat, tweeted Wednesday afternoon. "Being sorry isn't enough."
Fellow Democrat U.S. Rep. Diana DeGette echoed Perlmutter's call to action, tweeting, "Congress has the power to help prevent these tragedies. Inaction is simply not an option, and we must work now to save lives."
Democratic U.S. Sen. Michael Bennet, a former superintendent of Denver Public Schools, issued an emotional response on Twitter Wednesday evening stating that "an entire generation" is "growing up in fear that their school will be next."
"My thoughts are with families of victims & first responders in FL, but I also know that thoughts are not enough," Bennet tweeted. "It's time for action."
Appearing Thursday morning on MSNBC's "Morning Joe," Bennet called on Congress to take a page from Colorado's playbook and pass legislation that prevents violent individuals from obtaining guns.
"It's important to close the loopholes that exist in the federal background check," he told co-host Mika Brezezinski. "That's what we've done in Colorado. You asked, 'Why aren't these possible in Washington?' It is a mystery. I come from a Western state. We have had horrible tragedies, terrible mass shootings in our state. We closed the gun-show loophole. We closed the internet loophole. We passed a law in our legislature that limited the size of magazines, and we should do the same thing in Washington.
"I challenge anyone in the United States Senate to come down here and make the case that Colorado's not safer for having kept guns out of the hands of murders, rapists and domestic abusers."
Democratic U.S. Rep. Jared Polis tweeted that his heart "sunk" after receiving word of Wednesday's shooting, but did not issue a call to action.
"My sincerest gratitude to the first responders who are doing their best to keep these children safe," he tweeted.
Wednesday's events left U.S. Rep. Doug Lamborn "heart broken," he tweeted, adding that his "thoughts and prayers" were with the community. Lamborn's Republican colleague, U.S. Rep. Mike Coffman, tweeted similarly Wednesday evening, stating, "Tonight communities across the US stand together with residents of Parkland and the brave first responders in that community." Republican U.S. Rep. Ken Buck tweeted that he was "devastated" and "praying." Republican U.S. Sen. Cory Gardner tweeted that he was "heartbroken" and "praying."
The Associated Press contributed to this report.