ANDREW MALCOLM: What Trump’s attack on Syria did – and did not – do.

Trump campaigned against U.S. military being a global policeman. This single strike doesn’t mean that’s changed. His justification was based on the paramount importance of U.S. national security.

“It is in the vital national security interest of the United States,” Trump said, “to prevent and deter the spread and use of deadly chemical weapons….Years of previous attempts at changing Assad’s behavior have all failed, and failed very dramatically. As a result, the refugee crisis continues to deepen and the region continues to destabilize, threatening the United States and its allies.”

It does mean, however, that America’s allies, especially Sunni Arab states like Jordan and Saudi Arabia that were awaiting U.S. leadership, are encouraged. The Saudis have even offered troops to fight ISIS.

It does mean that bad actors such as Syria, Iran, Russia and even loopy North Korea must now factor in Trump’s proven willingness to exercise American clout when he perceives a national security threat.

After the Sarin gas attack with photos of babies gasping for air, Trump acted swiftly and decisively. But not as critics fretted last year, wildly. He could have attacked all six Syrian airfields. He could have ordered Special Forces to simultaneously move in eastern Syria.

Instead, Trump targeted only the specific airfield that launched the gas attack. It was a measured response. No new ground troops. Not even pilots risking capture.

“Measured responses” don’t win wars, but that’s beside the point. The message was sent that the use of chemical weapons won’t be tolerated, but not sent strongly enough to kill Assad and turn Syria into another Libya.