On Monday, we’ll enjoy – or endure, depending on your point of view – the third and final presidential debate of this election season.

As you’ve watched Barack Obama and Mitt Romney spar, you’ve also had the option to join The Atlanta Journal-Constitution’s Kyle Wingfield, Jay Bookman and Jim Galloway, our editorial columnists and Political Insider, who’ve been tweeting and blogging during the debates.

And our Politifact team has been providing fact checks of statements made during the debates, and will be busy again this time.

You’ve likely been debating about the debates yourself: Who won, who sounds better, who looks more presidential?

I took a little time last week to talk to a friend and a long-time debate observer to get his take on this year’s debates.

John Splaine is an adjunct professor at Shepherd University in Shepherdstown, West Virginia. He taught at the University of Maryland for nearly 30 years before he retired from that school. He’s been a consultant to C-SPAN and is an expert on presidential debates. In the mid-1990s, he wrote a book, “The Road to the White House Since Television.”

In the past, Splaine has emphasized to me that presidential debates typically change few minds. And typically the debates don’t allow for much true debate.

He says it’s actually kind of simple:

About 40 percent of us have made up our minds to vote for the Republican before the debate. Another 40 percent have decided to vote for the Democrat. We watch the debate and believe our guy won.

The key to the whole thing is undecided voters. And many of them are unlikely to be watching. So how do they decide who won? More about that later.

Splaine says important things have been different this time, making the presidential debates similar to some key historical debates. And the guy knows debate history. He wrote a companion book to C-SPAN’s re-enactments of the 1858 Lincoln-Douglas Debates. But his points highlight more recent history.

In the first televised presidential debate, Splaine said, we saw what he calls “The Kennedy Effect.”

In the famous 1960 debate, if the polls were to be believed — a qualifier that Splaine gives to all presidential races — a youthful John F. Kennedy changed the race with Vice President Richard Nixon.

According to Splaine, an important thing helped Kennedy: he was on stage with the vice president and viewers could compare the two. Though Kennedy wasn’t as well-known as Nixon, he looked more presidential.

Splaine also points to the 1980 Carter-Reagan debate as one that had a big impact on the race. Reagan, a former Hollywood movie star who Democrats were trying to paint as a right-wing extremist, came across as a guy people could see as president.

In Splaine’s view, this year’s first presidential debate fits into history in a similar way. If you believed the polls, they were indicating that Obama was leading. And the president was certainly better known to most Americans – especially to undecided voters.

But when former Massachusetts governor Romney was on stage with the president, Romney was able to look like a guy who could be president to many people who hadn’t seen that before.

And, again if you believe the polls, the dynamic of the race changed.

“If people like a contest, you’ve got it,” Splaine said. “These debates reshaped the race.”

In the second presidential debate, Splaine said, Obama had to try and stop Romney’s momentum, which shaped the dynamic that night.

“The second debate stopped the bleeding for Obama,” he said.

So what should we expect on Monday night?

Splaine suggested paying attention to a few things:

• This debate, moderated by CBS News’ Bob Schieffer, will focus on foreign policy. Schieffer has said he’ll ask about the Middle East, Afghanistan, terrorism, China and America’s role in the world.

• A sitting president has an advantage in this subject area. Obama has access to more information and deeper knowledge of national security issues.

• What issues will Romney pursue? He will have to choose carefully.

And one more thing. Both candidates need to study and show a command of their information. For example, they could get asked the name of a foreign leader in a foreign policy debate.

“There a greater chance of making a mistake,” Splaine said. He pointed out Gerald Ford’s famous gaffe in 1976, when he said: “There is no Soviet domination of Eastern Europe.”

If Obama or Romney make that kind of mistake, those undecided voters, most of whom are unlikely to be watching – after all Monday Night Football will be on – might make a decision based on that kind of debate-history sound bite. Because a big debate moment — including a gaffe — reaches a much wider audience than the debate itself.