As Mitt Romney and President Obama huddle with their debate coaches this weekend, they will each have to make a simple but potentially critical decision before Wednesday's faceoff.

What do they call each other?

Will it be "Mr. President" or "the president" when Romney refers to his rival on stage? Will Obama talk about the policies "the governor" wants to pursue? Or will he talk about the impact of those policies from "my opponent"?

Will there be less formal moments, when "Mitt" and "Barack" slip out?

Millions of people will be watching the two men in one of the very few direct interactions they will have during the 2012 campaign. Among the things being scrutinized: How much respect will each contender pay to his rival?

"There's a certain amount of decorum that we expect in our debates," said Brett O'Donnell, one of the Republican Party's top debate coaches. "The reference that they use for each other is a beginning point for that decorum."

The nation's capital is famous for its fake friendliness; think of how often senators heap praise on their "good friend, the gentleman from Ohio" just before skewering the Ohio senator's motives and killing his legislation with a parliamentary maneuver.

Presidential debates are no different. They are among the highest-stakes moments in U.S. politics. Yet they demand smiles and handshakes at the beginning — a demonstration of respect and friendliness often at odds with the tough talk that often follows.

There have been few occasions in modern political history of outright nastiness or scorn when it comes to how presidential candidates refer to each other during debates. Still, campaigns have often made subtle choices as they seek an advantage.

During the first debate between Obama and Sen. John McCain of Arizona in 2008, Obama all but ignored McCain's decades as a senator.

Almost every time Obama referred to his rival during that debate, he simply used his first name.

"I don't know where John is getting his figures," Obama said at one point. Another time, he said, "John, nobody is denying that $18 billion is important." Later, he spoke directly to McCain, saying, "John, 10 days ago, you said that the fundamentals of the economy are sound."

In all, Obama used McCain's first name 25 times. By contrast, McCain referred to Obama as "Senator Obama" or "the senator" each time.

"It was a backhanded compliment," O'Donnell said, recalling Obama's use of McCain's first name. "On the outside, he was being friendly, trying to be comfortable. It was a way of being respectfully distrustful."

Three weeks later, in the third debate of the 2008 campaign, Obama had apparently thought better of his choice. He called McCain "John" only once, referring to him as "Senator McCain" throughout the rest of the debate.

That same year, Sarah Palin, a former governor of Alaska and McCain's vice-presidential nominee, asked her rival, Sen. Joseph Biden, "Hey, can I call you Joe?" while shaking his hand at the debate's opening.

She went on to call him "Senator" during most of the debate, but she did drop the formality when responding to Biden's criticism of the previous Republican administration.

"Say it ain't so, Joe," Palin said.

Debate coaches often suggest candidates do whatever they can to subtly undermine their rival's experience and stature. In 2004, President George W. Bush repeatedly referred to Sen. John Kerry as merely "my opponent," even when referring to Kerry's Senate votes.

Bush used the same approach four years earlier, when debating Vice President Al Gore. Sometimes he called him "the vice president," but often switched to "my opponent." Gore stayed with the formal "Governor Bush," reminding all who were watching of the limits of Bush's experience.

Bush's father, the first President Bush, always referred to Michael Dukakis as "Governor Dukakis" in 1988. President Carter was careful to say "Governor Reagan" during their 1980 debates. In fact, most presidential candidates seem to adopt that careful approach: Be respectful by using a proper title that does not risk offending anyone.