The FBI said Friday that someone who knew Cruz called an agency tip line on January 5 and left information about Cruz's "gun ownership, desire to kill people, erratic behavior, and disturbing social media posts, as well as the potential of him conducting a school shooting".
She then ran through a list of the pro-gun lobby's talking points - for example, that "a good guy with a gun stops a bad guy with a gun", that no law could ever stop a madman intent on killing - answering each argument with "We call BS".
Survivors of the shooting and friends of victims reacted sadly and angrily to Trump's tweet.
Investigators described him as a troubled teenager who posted disturbing material on social media and had been expelled from the high school for "disciplinary reasons", Broward County, Florida, Sheriff Scott Israel said.
He pledged to work with state and local officials to "help secure our schools and tackle the hard issue of mental health", adding that safe schools would be a key focus when he meets with governors and state attorneys general later this month. Wayne LaPierre, one of the leaders of the NRA, is also scheduled to speak.
Earlier Saturday, after the rally held by survivors calling for action on guns, the president tweeted "why didn't the Democrats pass gun control legislation when they had both the House & Senate during the Obama Administration", adding, "Because they didn't want to, and now they just talk!"
"The question on whether or not people should be allowed to own an automatic weapon is not a political one". White House aides advised against golfing too soon after the shooting. Trump said in the first of several contentious tweets over the past 12 hours. Their "March for Our Lives" is planned March 24 in Washington.
Schiff, speaking on CNN's "State of the Union" program, said details of the indictment provided "overwhelming and unequivocal" evidence of the threat from Russian interference and countered Trump's assertions that the Russia investigation was a "hoax".
"You're the President", Hogg said.
But previous gun tragedies have not produced action in Congress.
Asked about the lack of action on NBC's Meet the Press Sunday, Sen. "Get back to the basics and make us all proud!" he tweeted. He also noted, though, the high bar to limiting gun ownership due to the Second Amendment. "And the right to keep and bear arms is a constitutional right".
Jimmy Kimmel sardonically fired back, "I hope the Federal Bureau of Investigation finds and prosecutes the complete A-hole who hacked the President's account and tweeted this". But we need leadership out of the executive.
"He's just messed up", Ciaramello said of Cruz, another JROTC member.
Florida Republican Rep. Carlos Curbelo responded, in part, by saying, "We've kind of inherited this world of binary choices where we either have to repeal the Second Amendment or have no gun-safety regulations whatsoever, and younger generations of Americans don't see the world that way".
In a marathon series of furious weekend tweets from Mar-a-Lago, Trump vented about Russian Federation, raging at the FBI for what he perceived to be a fixation on the Russian Federation investigation at the cost of failing to deter the attack.
"Because they didn't want to, and now they just talk!" was the president's response, even though Republicans blocked several Democratic proposals after the 2012 massacre at Sandy Hook Elementary School in CT.
Organisers behind the Women's March, an anti-Trump and female empowerment protest, called for a 17-minute, nationwide walkout by teachers and students on March 14.