President Barack Obama on Friday nominated former Pentagon general counsel Jeh Johnson to succeed Janet Napolitano as Homeland Security Secretary. If confirmed, Johnson, 56, a former federal prosecutor, would be the first African-American person to lead the Department of Homeland Security. Obama said Johnson had a deep understanding of the threats and challenges facing the United States. At the Pentagon, Johnson oversaw the increased use of unmanned drone strikes, the revamping of military commission to try terrorism suspects and the repeal of the ban on gays in the military. His potential predecessor Napolitano stepped down last month to lead the University of California.