Signaling a generational change at one of the nation’s most influential newspapers, the new publisher of The Washington Post on Monday selected an outsider as the paper’s top editor. Marcus W. Brauchli, a former top editor of The Wall Street Journal, will become the executive editor of The Post on Sept. 8, at a time of great upheaval in the industry. At age 47, he is young enough to remain in place in for many years, working alongside the publisher, Katharine Weymouth, who is 42 and has been in her job for five months. He will succeed Leonard Downie...