WASHINGTON (AP) — The Biden administration’s head of Homeland Security is defending a policy of allowing unaccompanied children crossing the southwest border to remain in the U.S. while quickly expelling most single adults and families. Homeland Security Secretary Alejandro Mayorkas issued a lengthy statement Tuesday on the response to the rising number of migrants apprehended along the U.S.-Mexico border. The Biden administration is continuing a Trump policy of quickly expelling single adults and families under a public health order due to the coronavirus pandemic. But it’s holding minors in temporary shelters until they can be placed with relatives or sponsors in the U.S. Mayorkas says the situation at the border is “difficult.”