After coming across the initial thread of intelligence earlier this year, U.S. officials, in regular consultation with the White House, developed a “detailed plan” for addressing the issue, as one source put it. That plan was presented several weeks ago to the White House, which has been debating with other agencies whether the potential security benefits outweigh the potential impacts on partners overseas.
DHS Secretary Jeh Johnson has the authority to unilaterally issue directives to airlines overseas, but agency heads like him generally prefer to have the backing of the White House when making big moves. After all, issuing such security directives carries both economic and diplomatic implications.
Getting foreign governments all on the same page is no easy task, and forcing authorities overseas to increase security measures demands more manpower and resources from those foreign governments and airlines. Nevertheless, while airlines overseas could refuse to comply with DHS security directives and drop U.S.-bound flights from their routes, economic pressures virtually eliminate that as an option.
This would not be the first time DHS has issued urgent directives to airlines overseas. In July 2006, TSA issued at least two "emergency amendments" to foreign carriers, detailing "enhanced security measures for all flights" to the United States. A month later, the U.S. and British governments disclosed that they had thwarted a plot to down several planes with liquid explosives hidden in carry-on luggage.
The latest potentially lethal partnership in Syria is at least part of what sparked an advisory to airlines earlier this year to look out for explosives-laden toothpaste tubes, cosmetics and shoes.
Since January, officials with access to the country's most sensitive intelligence have warned publicly that hard-to-detect "technologies and techniques" were being exported to Syria, that foreign fighters from the West were "learn[ing] new things" and "build[ing] new relationships" in Syria, and that "training complexes" were popping up there to prepare Western fighters for terrorist attacks against their home countries.
More recently, Comey, the FBI director, said the U.S. government is spending "a tremendous amount of time and effort trying to identify" anyone who's gone to Syria, but "the challenge" is not missing anyone.