Why didn't the administration act three days before the launch of chemical weapons, according to its own chronology?

"Zanders said he also was surprised about the revelation that the U.S. had collected intelligence from multiple sources in the three days prior to the attack that showed Syrian weapons personnel were preparing chemical munitions. "Was this something the U.S. had in real time or did it get it (and) appreciate its significance after the attacks?" he said. "If not, then my question is why the Obama administration did not issue a public warning to deter the attack?" "