Last month, President Obama nominated Gen. Lloyd Austin to succeed Gen. James Mattis as the head of U.S. Central Command. The choice and its timing immediately raised questions about Mattis’ future, particularly given his standing as one of the most revered military leaders of his generation. Mattis was typically stoic when I approached him for a response. “I’ll remain focused on my job at CENTCOM for now and figure out the rest later,” he said in an email. U.S. military officials have speculated for months that Mattis could leave his CENTCOM post by this summer and join civilian life. Now,…