Department of Homeland Security Chief of Staff Karen Olick resigned Monday amid the migrant crisis at the southern border and an influx of Afghan refugees to the United States, Politico reported. Olick, who serves as the chief of staff to Homeland Security Secretary Alejandro Mayorkas, plans to move on from the position at the end of September, according to the report Monday. Jennifer Higgins, associate director of refugee, asylum and international operations for U.S. Citizenship and Immigration Services, is expected to step into the role in an acting capacity until the Biden administration appoints someone else. Olick “has decided to resign her position and pursue new opportunities,” Mayorkas said, according to Politico. “We are grateful to Karen for her service during the critical first nine months of the new Administration,” he said. The DHS has struggled to manage the increasing number of migrants arriving at the southern border. The agency also has tried to manage and mitigate other crises, including the arrival of thousands of Afghan allies in the U.S. and the aftermath of Hurricane Ida.