A former Obama aide ripped President Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE for criticizing the FBI following the Florida high school shooting and for saying the bureau was spending too much time trying to prove Russian collusion with the Trump campaign.

"Exploiting the death of children to undercut the Mueller investigation. I am speechless," Tommy Vietor, who served as a spokesman for former President Obama's National Security Council, tweeted.

Exploiting the death of children to undercut the Mueller investigation. I am speechless. https://t.co/QGIZV8RJyO — Tommy Vietor (@TVietor08) February 18, 2018

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Trump late Saturday tweeted about the shooting, saying it was not acceptable that the FBI missed "many signals" sent out by the alleged gunman.

"Very sad that the FBI missed all of the many signals sent out by the Florida school shooter. This is not acceptable. They are spending too much time trying to prove Russian collusion with the Trump campaign - there is no collusion. Get back to the basics and make us all proud!" he tweeted.

The FBI said Friday it failed to follow "protocols" when it received a tip earlier this year about 19-year-old Nikolas Cruz, who allegedly went on a rampage last week in Parkland, Fla.

A person close to Cruz called the FBI's public tipline and raised concerns about him in January, the bureau said.

But the FBI never reported the tip to its Miami field office or investigated the claim, it added.

Multiple lawmakers have called for Congress to act to prevent another tragedy following the shooting, in which 17 people were killed and 14 others wounded.