I’m not sure we’ll ever get a philosophically satisfying answer for why Gen. James Mattis, three years retired from active duty, deserves a legislative exception from the law requiring any secretary of defense appointee to have been retired for at least seven years. If someone can get a waiver just because he or she is exceptionally well-respected, then the law is less a law than a symbolic statement of ideals. We may not be able to get a decent logical answer for why Mattis deserves a waiver. But we can get strong practical reasons for why Mattis deserves it, chief among them: Donald Trump needs the most qualified people by his side, rules be damned, because he is galactically unprepared for the office and liable to make stupid national-security decisions. And if Mattis is the guy who can talk sense into him? Clear the path.