As I explained in my last piece, this week's ASEAN summit is a major challenge for Secretary of State Rex Tillerson.

Yet it's also a serious challenge for those who protect him.

After all, the Philippines faces a highly capable array of Islamist terrorist threats. As I noted in June, the Islamic State now tops this list. Holding fealty from longtime terrorist facilitators and fighters, ISIS threatens the Philippines with complex, high-casualty plots.

As they travel to Manila, this threat will be foremost on the minds of the Bureau of Diplomatic Security. Responsible for protecting the U.S. Ambassador to the U.N., U.S. officials on foreign trips, and cabinet-level visitors to the United States, BDS agents have a crucial job. But no BDS mission is more important than protecting America's chief representative to the world, the secretary of State.

Representing American power and prestige, Tillerson represents a priority target for foreign adversaries.

Still, in protecting Tillerson, the BDS faces a unique challenge. As a diplomat, the Secretary of State needs to be accessible. Whenever he travels abroad, Tillerson is expected to meet with a large number of foreign politicians, activists, and bureaucrats. But unlike the Secret Service, which has significant control over who can approach President Trump, the BDS must defer to diplomatic protocol. Reflecting as much, BDS agents aren't just federal law enforcement officers; they are diplomats.

Two videos indicate the BDS' particular difficulty in balancing diplomacy and protection.

The first video shows Tillerson arriving at a diplomatic event in New Zealand, surrounded by various officials, journalists and others. It's an uncomfortable situation for any protection team. Were Trump the guest, the Secret Service could have been far more restrictive about those around him. Yet because Tillerson is a diplomat, the BDS must give greater deference to local authorities.

The second video, from February, shows Tillerson's motorcade arriving at a German hotel. But unlike the New Zealand arrival, this event is not diplomatic in nature. That gives the BDS far greater control over Tillerson's security. The differences are obvious. As his car pulls up, Tillerson's protective detail wait to establish formation before his protective detail's agent-in-charge/shift supervisor opens his car door. The site agent (in charge of security/logistics at each site) then quickly guides Tillerson — surrounded by BDS agents — into the hotel. It's clinical, efficient, and highly secure. A testament to BDS professionalism.

But it's also rare.

As in the first video, the BDS must normally defer to diplomacy. And that will certainly be the case in Manila. Tillerson will need to be available to foreign delegations and their bureaucrats. That means a lot of unknown faces moving around him at all times. The BDS must regard all these individuals as threats. But as they manage possible threats, the BDS must avoid upsetting Tillerson's hosts or any dignitaries he deals with. Like their American opposites, foreign government ministers have egos. If the BDS upsets these egos, they risk harming American interests.

As I say, it's an immensely tough job. Most of us might enjoy a trip to Manila. The BDS, however, will not.

Note: An earlier version of this article suggested that the Bureau of Diplomatic Security protects the UN Secretary General. In fact, the BDS only protects the UN Secretary General on certain trips inside the United States.