Complex sentence: From July 2003 until his departure in December 2005, Oberman was TSA's Assistant Administrator for Transportation Threat Assessment and Credentialing, where he was responsible for the agency's programs that identify known or potential terrorist threats working in or seeking to access the transportation system.
Split into simpler sentences: From July 2003 until his departure in December 2005, Oberman was TSA's Assistant Administrator for Transportation Threat Assessment and Credentialing. He was responsible for the agency's programs that identify known or potential terrorist threats working in or seeking to access the transportation system.