Last week, the Republican presidential campaign devolved into arguments over trivial issues wrapped in terms of "political correctness," a term used to mock people who exercise intentional good manners, decency and fairness.

The national debt is $19.2 trillion. The planet is warming at alarming rates. The public education system is in crisis. The middle class is struggling to stay afloat. Tensions simmer in the Korean peninsula and Middle East. Refugees who don't drown by the hundreds in the Mediterranean are overwhelming Europe.

And what are the Republican Party's two leading candidates arguing about? Political correctness, as in which bathrooms people should use and whose face should appear on the $20 bill.

Naturally it was Donald Trump who started it. He's gotten a lot of mileage from references to ''this politically correct crap," using PC fatigue as an excuse to insult Muslims, Mexican immigrants, women and people who don't say "Merry Christmas." He plays directly to a certain segment's exasperation.

"?'Political correctness' are the two words that best respond to everything that a conservative feels put upon," GOP pollster Frank Luntz told the Washington Post.

Trump found new fodder on Wednesday when the U.S. Treasury Department announced that Harriet Tubman would replace Andrew Jackson on the front of the $20 bill. It's part of a wider, and long overdue, effort to include women and African-Americans on U.S. currency.

The next morning on the "Today" show, Trump said the move was "pure political correctness." He said that Tubman, with whose history as a 19th century abolitionist he claimed to be familiar, was "fantastic" and deserved to be honored. But he suggested we do the $2 bill.

But replacing the white guy on the twenty with a black woman? Pure political correctness.

Jackson, known as Old Hickory, was something of a populist himself, like Trump. He rode support from westerners and farmers to the White House in 1829. At the risk of being accused of political correctness, we should note he gained that support by wiping out Native Americans on the early frontier.

But then, on the question of North Carolina's controversial no-using-bathrooms-that-don't-match-your-genitalia law, Trump said people should be allowed to use whatever bathroom they feel comfortable using.

Texas Sen. Ted Cruz, trying desperately to catch up, pounced. "Let me ask you, have we gone stark-raving mad?" he told a rally in Maryland. "This is political correctness. This is nonsense."

Either Trump misread the fervor with which this issue resonates with the GOP base, or he accidentally said something he really believes, but he handed Cruz a solid-gold opportunity. By Thursday night, Trump was walking back his comments, telling Fox News' Sean Hannity, the arbiter of modern GOP orthodoxy, that states should make the decision for themselves.

Yes, silliness is entertaining. But entertainment value is a sorry measure of someone's ability to lead a nation.

REPRINTED FROM THE ST. LOUIS POST-DISPATCH