It’s not clear exactly when Trump learned of the alert, although presumably the president would be informed of any potential threat immediately.
White House deputy press secretary Lindsay Walters said in a statement that the president had been “briefed on the state of Hawaii’s emergency management exercise.”
“This was purely a state exercise,” she added.
A White House official told CNN that the president was briefed in person by national security adviser H.R. McMaster, deputy national security adviser Ricky Waddell and White House chief of staff John Kelly.
A senior administrative official told Politico that there was no military response around the president during the incident because there was no actual threat detected by the military. The source also said that Trump’s Cabinet hasn’t yet tested plans for how they would respond in such an attack
Former Pentagon official Col. Morris Davis criticized the president in a tweet for continuing his round of golf on his “taxpayer funded vacation” as Hawaiians “braced for a ballistic missile strike.”
Source : http://www.huffingtonpost.co.uk/entry/trump-golf-hawaii-missile-alarm_us_5a5a9201e4b04f3c55a32242226