[Victor Davis Hanson is a classicist and historian at the Hoover Institution, Stanford University, and the author, most recently, of The Father of Us All: War and History, Ancient and Modern.]

The president of the United States has it hard enough without needlessly wading into, and fanning, local controversies. The economy is battered by sluggish growth, high unemployment, record annual deficits, and near-unsustainable national debt. Over 50 percent of the people now disapprove of Barack Obama’s handling of these problems.

So why weigh in on hot-button issues that can only polarize people without solving anything?

Last summer, Harvard professor Henry Louis Gates, a scholar of African-American literature and history, got into a silly dispute with a local policeman. For some reason, President Obama, the leader of the free world, rushed to judgment and gratuitously announced that police sergeant James Crowley and the local Cambridge, Mass., police had acted “stupidly.” For relish, he added that police wrongly stereotype in general. Obama supporters wrote off the entire psycho-drama as a “teachable moment.”

Arizona recently passed a bill designed to enforce existing immigration law and stop the enormous influx of illegal aliens into the state. Various groups, including the federal government, quickly made plans to sue the state. Yet various polls indicated that 70 percent of Americans agreed with the Arizona law, and dozens of states were planning similar legislation....