How DHS's threat to cut customs processing in sanctuary cities could snarl air travel everywhere Markwayne Mullin, the new DHS secretary, has said he is considering cuts to customs agents at international airports in US cities that do not cooperate with his department's deportation efforts. Kent NISHIMURA / AFP via Getty Images If the Department of Homeland Security follows through on a threat to yank customs agents from major airports housed in sanctuary cities, industry watchers say fliers would face travel chaos that would make long TSA lines look like child's play. Airlines would be forced to redraw route maps on the fly — triggering all kinds of questions about staffing, facilities, and travelers themselves. Consider, for instance, just one flight: American Airlines Flight 101, scheduled to depart London-Heathrow each day at 10:30 a.m. and land at New York's JFK at 1:20 p.m. Where to land the plane?…