WASHINGTON — President Obama plans to nominate Jeh C. Johnson, who framed many of the administration’s national security policies as the Defense Department’s general counsel during Mr. Obama’s first term, to become the next chief of the Homeland Security Department, according to administration officials. Mr. Johnson has little experience with some of the issues Janet Napolitano faced, like border security, immigration and cybersecurity. During his tenure at the Defense Department, he spearheaded the end of the “don’t ask, don’t tell” law that had barred gays and lesbians from serving openly in the military. He also shaped the Obama administration’s policies...