"The F.B.I.’s admission that it did not act on a tip that Mr. Cruz had a 'desire to kill people, erratic behavior, and disturbing social media posts,' could open up a new avenue of attack for political opponents seeking to discredit the bureau’s work...."

"After the shooting, conservative news media said that the F.B.I. could have prevented the attack if it had not been spending so much time looking into Russian election interference.... This is not the first time that the F.B.I. has come under fire for being aware of a threat and failing to stop an attack. Congress criticized the bureau for failing to stop the 2009 mass shooting at Fort Hood in Texas, where the shooter was known to the F.B.I. The F.B.I. also knew of one of the brothers who carried out the 2013 Boston Marathon bombing, but did not stop that attack. After those fumbles, F.B.I. investigators compared themselves to hockey goalies, who are fielding a relentless barrage of pucks. Sometimes, they said, they cannot keep things from making the net."

From "F.B.I. Was Warned of Florida Suspect’s Desire to Kill but Did Not Act" (NYT).

ADDED: Here's the FBI's statement. Excerpt:

The caller provided 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. Under established protocols, the information provided by the caller should have been assessed as a potential threat to life. The information then should have been forwarded to the FBI Miami Field Office, where appropriate investigative steps would have been taken. We have determined that these protocols were not followed for the information received by the PAL on January 5. The information was not provided to the Miami Field Office, and no further investigation was conducted at that time.