Political conventions are supposed to be about controlled hysteria.

Thousands of people cram into a hall. Music throbs. Speeches blast. And in the case of the Republican convention that opened Monday afternoon in Cleveland, the a cappella children’s choir on the stage was considerably more diverse than the delegates on the floor.

No matter. Conventions are about image building. Reality can be left for another time and another place.

In the modern era, in which delegates are chosen by primaries and caucuses, conventions have a built-in silliness. It is like watching the Oscars already knowing what names are in the envelopes.

In Cleveland this week, there are but two names in the envelopes: Donald Trump and Mike Pence. Where’s Mike Pence? Hey, Pence, get over here. Didn’t anybody give you your cues? No matter. Somebody on the Trump campaign will get around to it.

The conventions are all show business, and the business of show business is to please the crowd. Scholar and media theorist Neil Postman wrote in 1985, “If politics is like show business, then the idea is not to pursue excellence, clarity or honesty but to appear as if you are, which is another matter altogether.”

This year, there is an added element to the conventions: Which party and which candidate can keep our citizens from being slaughtered and our police officers from being slain? Which can delay, if not halt, the march of horror across the globe and terror through our land?

Which, for pity’s sake, can let us wake up in the morning, click on the TV or boot up the computer and not feel a cold sweat before the screen comes to life to show us how many of our fellow human beings will not be coming to life at all.

Which can give us a day — just one day! — of life without foreboding and dread?

“We must not turn our backs on each other,” Hillary Clinton said about Baton Rouge, Louisiana, where a gunman killed three police officers Sunday.

Hell no. Don’t turn your back on anyone these days before you know what he is carrying in his hands. And if it’s a gun and you live in a state where openly carrying a gun is legal, your choices are limited.

But “duck and cover” is a good one.

And “shelter in place” is becoming our new national motto.

President Barack Obama has asked politicians to dial down the rhetoric of hatred and division and to also not lose hope. In Dallas, where five police officers were slain July 7, he said: “I’m here to say we must reject such despair. I’m here to insist that we are not as divided as we seem. And I know that because I know America.”

Donald Trump says we don’t even know Barack Obama. “I watched the president, and sometimes the words are OK, but you just look at the body language. There’s something going on,” Trump said on “Fox & Friends” Monday out of deviousness or ignorance or both. “Look, there’s something going on, and the words are not often OK, by the way.”

The words are not OK. The body language is not OK. And by the way, did they ever do radiocarbon dating on his birth certificate?

According to the most recent Washington Post/ABC News poll, released Monday, 64 percent of Americans have an unfavorable view of Trump and 54 percent have an unfavorable view of Hillary Clinton.

The bar for the presidency isn’t just low; it’s virtually subterranean.

But in Cleveland, the show begins.

In a news conference, Jeff Larson, the CEO of the convention, was peppered with questions about security. But he kept his eye on the ball.

“We are very proud of our podium,” he said, pointing out that a 10 million-pixel image was being projected on a 1,711-square-foot digital screen. The lighting grid weighs 140,000 pounds, and there are 647 moving light fixtures that he can use to affect “the color and tone of the convention.”

Principles? Policies? Platform planks? They would probably take up too many pixels.

In 1996, Ted Koppel and his “Nightline” crew made headlines when they packed up in the middle of the Republican convention in San Diego and went home.

“This convention is more of an infomercial than a news event,” Koppel said. “Nothing surprising has happened. Nothing surprising is anticipated.”

Koppel was expecting a surprise? That’s why he schlepped to San Diego? What planet did he grow up on?

Nobody in Cleveland is expecting a surprise this week. Few want one.

Nice, quiet, humdrum and bloodless will be just fine.

Roger Simon is Politico’s chief political columnist. His new e-book, “Reckoning: Campaign 2012 and the Fight for the Soul of America,” can be found on Amazon.com, BN.com and iTunes.

Photo: People stand on the floor of the Republican National Convention in Cleveland, Ohio, U.S., July 17, 2016.   REUTERS/Mario Anzuoni