President Donald Trump said the FBI "missed all of the many signals" sent by the suspect in the Florida school shooting.
Trump says on Twitter on Saturday night: "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."
The FBI received a tip last month that the suspect in the Florida school shooting had a "desire to kill" and access to guns and could be plotting an attack.
But the agency said on Friday that agents failed to investigate.
Florida Governor Rick Scott has called on FBI director Christopher Wray to resign.
Trump has been a frequent critic of the FBI, accusing it of partisan bias.
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