For decades, it was a matter of conviction among political professionals that most Americans didn’t begin to focus on the presidential election until after the World Series.

That’s just one of many old chestnuts that have been chucked out the window in the new age. Bill Mazeroski’s walk-off home run to win the seventh game of the 1960 World Series occurred on Oct. 13, some 26 days before the election. The seventh game of this year’s World Series is scheduled for Nov. 1, six days before the election. The old formula won’t work anymore.

So the new shorthand is that the decisive phase of the election begins with the first debate, which occurs Wednesday night at the University of Denver.

It may seem that presidential campaigns have several resets, most recently the dueling national political conventions. There’s some truth to that. But the twin acceptance speeches of late summer were campaign set pieces, with every element — the venue, the setting, the length, the topic, all of the atmospherics, including the podium and the teleprompters — controlled by the candidates’ hired hands. There were no uncertainties, no hidden obstacles, no opportunities for forced errors.

Debates are different

Wednesday is different in every way. The campaigns have been involved in negotiations with the bipartisan Commission on Presidential Debates that oversees the events and regulates the conditions. But the difference is that a live, televised presidential debate is an opportunity to see candidates interact with each other, handle unanticipated thrusts and parries, and in rare but revealing occasions show spontaneity.

It is great theater, of course. But it is also illuminating theater, even if some of the best lines (“There you go again,” former Gov. Ronald Reagan said to President Jimmy Carter in 1980) have been scripted.

There have been several revealing moments, unforgettable elements of debate folklore. Like the exasperating sighs of Vice President Al Gore during his debate with Gov. George W. Bush in Boston in 2000. Or the excruciating, awkward 27 minutes when President Gerald R. Ford and former Gov. Jimmy Carter stood stiffly at their lecterns during a power outage in the 1976 debate in Philadelphia.

And, of course, the devastating glimpse of President George H.W. Bush looking at his wristwatch in Richmond, Va., in 1992, as if to suggest that he couldn’t wait to get off the stage.

“I saw him look at his watch,” Clinton told Jim Lehrer in an interview in 2000. “And I — I thought, I felt, when I saw it, that he was, you know, uncomfortable in that setting and wanted it to be over with.”

Changing history?

No one knows for sure whether debates change history. An enduring piece of conventional wisdom is that Sen. John F. Kennedy won the 1960 election because he looked robust and appealing in his crisp blue suit in his first debate, while his opponent, Vice President Richard M. Nixon, looked fatigued and wan, especially because he was wearing a gray suit.

“We saw them with our naked eyes,” recalls Sander Vanocur, the veteran NBC newsman who is the only person still alive who took part in the 1960 debate. “Kennedy did not sweat. Nixon did a little sweating. It seemed as though Nixon — not too often but once in a while — looked to Kennedy for approval. But not everybody saw it that way.”

The impact of this debate — and whether in fact the people who saw it on television thought Kennedy had won while those who heard it on the radio thought that Nixon had won — has itself been a subject of debate for a half-century. But there is no debate on this: It’s not optimal to appear to perspire or to fade into the background in a gray suit.

A separate debate has sprouted in recent years, questioning whether these events matter at all. “What history can tell us is that presidential debates, while part of how the game is played, are rarely what decide the game itself,” John Sides, a George Washington University political scientist, wrote in the current Washington Monthly.

Sides cites several studies — plus a 1960 Gallup Poll showing that Nixon led by a single point beforehand and fell behind by 3 points afterward, which may be statistically insignificant — to support his argument. Vanocur now calls the debates “the odes of October,” adding in a telephone conversation, “They have become too much of an event, rather than a substantive turn in politics.”

But they are part of the process, and it is impossible to say in advance what might become an important campaign symbol in retrospect. Some debate episodes inevitably stick out, as both of the 2012 candidates know well.

Mitt Romney’s remark that the way his 2002 Massachusetts gubernatorial rival, Shannon O’Brien, characterized his views on abortion was “unbecoming” led to a contretemps over whether he was insulting or patronizing to women. Sen. Barack Obama’s remark that his 2008 Democratic rival Sen. Hillary Rodham Clinton was “likable enough” led to a flurry of critiques that he was condescending, insulting or unfeeling.

Does any of that matter?

Wednesday’s debate will include six 15-minute segments, half of them on the economy. One will be on the role of government, and here the two candidates might provide some valuable insights into their philosophy. Earlier this month, The Associated Press and the National Constitution Center released a poll showing that only two in five Americans believe the government is assuring the well-being of all Americans.

Some searching questions

That finding suggests a series of searching questions, examining whether the candidates believe the government is failing to address Americans’ needs (which might mean that it is incompetent, or needlessly bureaucratic, or the captive of special interests), or whether they believe the current conception of the government’s role is inappropriate to the times (which might mean Americans expect too much from Washington, or that an expansive view of government has dulled the public’s sense of responsibility and independence, or that the government’s role is about right for today’s circumstances).

One final thought before the opening bell: Whether presidential debates change the outcome is probably a lot less important than whether they inform the electorate. This is presidential politics, not a World Series game. In fact, this year the debates will be over before the Series is.