A failure to do so will lead to Somalia returning to a safe haven for international branches of al-Qaida, says Carson, now a senior adviser to the president at the U.S. Institutes of Peace.
"We will see a resurgence of not just al-Shabab, but al-Qaida East Africa, which has largely not been discussed," he says.
"This is an international issue, not just a Somali issue," he says. "It shouldn't be seen simply as an attack on Kenya and the Kenyan people. It should be seen as an attack on all those who are peace loving and all those who are fighting violent extremists and all those who want to see a return of stability to Somalia."
News coverage of the Saturday attack has granted al-Shabab added publicity, says Carson, adding, "It should not in fact weaken international resolve. It should not undermine the Kenyan support and [support] for AMISOM. It should not undermine regional support."
"The alternative is for this to get substantially worse again," he says.