Rahm Emanuel is, by any reasonable standard, a difficult man to beat. He orchestrated the Democratic Party's historic takeover of Congress in 2006, helped Barack Obama get elected in 2008, helped push health care reform through Congress in 2010 and just one year later, trounced all comers in the Chicago mayoral race.

Since taking that job, the 53-year-old Emanuel, nicknamed "Rahmbo", has thrown himself into another competitive realm—triathlon—where he's posted a series of impressive-sounding finishes in his age...