Acting Commissioner of Customs and Border Protection John Sanders revealed he resigned from his position on Monday in an internal memo to staffers. Sanders’ resignation, which is effective July 5, comes amid increased migrant flows to the U.S.-Mexico border and increased scrutiny over the safety of migrant children. In the emotional memo, Sanders reminisced on his time at the agency, saying it transformed him “professionally and personally.” Sanders wrote that the people he met “embraced and welcomed me in a way that was new to me—in a way that was truly special. To this day, I get choked up when speaking about it and I can’t adequately express my thanks.” Sanders did not give a reason for his departure in the letter.