My Latest in FP-- Honoring Chris Stevens : How the U.S. ambassador killed this week in Benghazi would have handled Libya.I met Ambassador Stevens on a handful of occasions. He was a casual and approachable man who boasted an impressive personal touch. His killing is not only a tragedy for both Americans and Libyans -- it is an attack on the engagement efforts between the two countries that he symbolized. It is no small irony that Stevens was killed as he was in Benghazi to open up an American cultural center. The likely long-term effect of this tragedy is that the U.S. mission in Benghazi will be shut down indefinitely, and plans to open a full consulate will be shelved. This is terrible news for the new Libya: Benghazi needs the mission, the cultural center, and the consulate to help overcome its decades of isolation under Muammar al-Qaddafi. Amid a week filled with tragedy, Libya took another step forward: On Sept. 12, the GNC convened to elect Mustafa Abu Shagur as prime minister, making him the first truly elected leader in the country's history. So joyous was this news that many Libyans resumed their habit of firing celebratory rounds into the night sky. Abu Shagur knows that the security situation must be his top priority, but building the fledgling Libyan security services will require active Western, and especially American, involvement. The goal of the consulate attack was to scare away just such assistance. To prevail over the terrorists, the United States must remain involved in Libyan capacity building. As I wrote back in February, there is much more the United States can do to help its Libyan allies, including serving as a matchmaker between Libyan officials and the American private sector and engaging with moderate Islamists and mainstream militias. Before the attack, there was a sense that Libya's sporadic violence consisted of regional or tribal conflicts that did not pose much direct threat to foreigners. It will be extremely dangerous if this healthy perception shifts. If America cuts and runs or lashes out in revenge, security and stability will deteriorate, foreign direct investment will dry up, and the Libyan economy outside of the oil sector will stagnate. That will provide fertile soil for the worst elements inside Libya to regain a foothold.Carefully crafted American engagement can help restore positive momentum to the political transition currently underway in Libya. In the wake of the savage killing of its ambassador, it’s time for the United States to double down.