President Trump's new homeland security secretary has suggested he will withdraw customs officers from the airports of Democrat-run "sanctuary cities" that protect undocumented migrants. The proposal from Markwayne Mullin, who was appointed to the role last month, would affect international travellers at many of the busiest airports in the United States, including JFK in New York, Los Angeles international airport and Denver international airport. "If they're a sanctuary city, should they really be processing customs into their city?" Mullin said on Fox News in his first interview since taking up the role.