Hillary Clinton, Donald Trump and the White House. (CLOCKWISE FROM TOP LEFT: /Carolyn Kaster/Associated Press; Ty Wright/Bloomberg; Raymond Boyd/Getty Images)

Kathleen Hall Jamieson is a communication professor and the director of the Annenberg Public Policy Center at the University of Pennsylvania.

Donald Trump has raised concerns about the fall debate schedule — two of the sessions are up against NFL games, certain moderators would be “unacceptable” — and accused Hillary Clinton of trying to “rig the debates.” On Monday, Trump said that he expected, “as of this moment,” to take part in all three debates, but his complaints have raised the possibility that he could become the first nominee since Jimmy Carter in 1980 to participate in just a single general-election debate — or even the only one since Richard M. Nixon in 1972 to spurn debates altogether. Either of those would be a disservice to voters, who would be cheated of valuable insight and deprived of the most important means of anticipating the contours of the next four years of governance.

In every televised face-off since Nixon and John F. Kennedy’s in 1960, watching the debates has increased viewers’ ability not only to distinguish between the candidates’ central positions but also to forecast what would happen during the winner’s presidency — in the form of Kennedy’s minimum-wage expansion, Bill Clinton’s “end welfare as we know it,” George W. Bush’s implementation of a prescription-drug benefit and Barack Obama’s tax hikes on high-income households.

Debate clashes also foreshadowed battles between Congress and the executive. George H.W. Bush’s debate opposition presaged the stalemate that tanked Clinton’s health-care plans in 1994, just as Al Gore’s 2000 attacks on George W. Bush’s personal Social Security accounts anticipated their defeat. By contrast, agreement between nominees can augur passage: Temporarily mothballing that “For Sale” sign was a smart bet after hearing Clinton and Bob Dole agree during a 1996 debate on exempting some capital gains on sales of a primary residence. Clinton signed the change into law the following year.

And the informational value of debates increases when candidates’ positions differ from the past stances of their party or its incumbent, as is the case this year with both nominees’ opposition to the Trans-Pacific Partnership (TPP) trade deal. Debates can also pinpoint evolving positions — for example, Trump’s shift from a temporary ban on Muslim immigration, to Clinton’s change in views on the “gold standard” TPP or fracked natural gas.

Multiple debates carry electoral advantages for the candidates themselves. Persuadable viewers sometimes skip a first debate but may tune into a second or third, for instance, if they prefer a more informal town-hall-style format. Nielsen data reveal that in 2012, only 14.9 percent watched at least some of all four debates.

Because it takes time to communicate complex issues, debates fit new pieces into a puzzle whose picture becomes clearer over the course of the encounters. The competing Social Security plans presented in 2000 offer a case in point. After the third and final presidential encounter, National Annenberg Election Survey data suggest that Gore’s argument that Bush would draw money out of the Social Security payment stream to fund personal accounts got through to additional voters. The centrality of that issue increased in the minds of those who watched the final debate — and with it their likelihood to support Gore, a factor that may have accounted in part for his popular-vote victory.

Multiple face-offs also give candidates a chance to recover from a single poor performance. In subsequent 1960 debates, Nixon was able to correct the visual dynamics that sabotaged him in the first meeting with Kennedy. After Ronald Reagan’s distracted performance in his first debate with Walter Mondale in 1984, the 73-year-old Republican nominee came back with his famous pledge not to hold his opponent’s “youth and inexperience” against him. Even Mondale laughed. Four years earlier, by contrast, Carter’s decision to face Reagan only once left the incumbent without a ready way to dispatch the question with which the challenger closed their only 1980 encounter: “Are you better off now than you were four years ago?”

Finally, fear of exposure by a knowledgeable opponent or persistent moderator concentrates the mind on briefings filled with policy knowledge. As a result, debaters are better informed than shirkers — a useful condition when renegotiating trade deals and seeking votes in Congress. And a president whose temperament, talents and plans survive the scrutiny of debate can argue that he or she is party to a compact that those who decided the election ratified.

So if Mr. Trump’s Labor Day hedge that “at this moment” he “expects” to take part in three debates is not an escape hatch, that’s good news all around.