Why isn’t Sen. Barack Obama (D-Ill.) doing better in the polls? As the convention opened, that question continued to grip political analysts and observers of all stripes.

Given a) the poor standing of President Bush and his Republican Party, b) the clear public preference for a sharp change in the fall, and c) the major advantage for Democrats over Republicans on the economy, taxes, gasoline prices, health, education, the environment and Iraq, the Democratic nominee should be leading by a wide margin over his GOP opponent. But Obama’s lead has been slender, averaging about 4 points or so over several months in national surveys.

The theories about the Obama gap between expectations and performance are multiplying. They include race, the Rev. Jeremiah Wright, Obama’s name and “exotic” background, his relative inexperience, the difficult and contentious nomination battle with Sen. Hillary Rodham Clinton (D-N.Y.), Arizona GOP Sen. John McCain’s tough negative campaign, and Obama’s failure, in the eyes of many Democratic operatives, to fight back with both barrels blazing.

There may be something in each of these elements. But there is another way to look at the state of play in the 2008 elections — the parallel of 1980.

1980, like 2008, was a change election. Jimmy Carter, running for a second term, was extremely unpopular as the election approached; his approval rating stood at 21 percent in mid-July, the lowest number recorded by Gallup since it started the measurement in 1938. Carter was subject to a stiff contest for his own party’s nomination from a liberal icon, Sen. Edward Kennedy (Mass.); while he skillfully beat back the challenge, his own convention was raucous and divided from start to finish.

Worse, Carter faced a horrible economy at home and American humiliation abroad. Economist Arthur Okun had coined the phrase “the misery index,” defined as the inflation rate and unemployment rate combined. Psephologist Richard Scammon’s axiom was that if the misery index were 10 or above, the incumbent and his party would be in serious trouble. As the election approached, the misery index was 20.

The main international story for the entire election season was the 52 American hostages held in Iran. ABC developed a nightly show to chronicle that saga. The show eventually morphed into Nightline — but during the 1980 campaign, it was called “America Held Hostage,” not the nightly slogan an incumbent president or party would want to have Americans hear.

The sour mood among Americans and the dismal approval ratings for the president should have given his main challenger, Republican Ronald Reagan, a comfortable lead in trial heats as the election approached. But that was not the case (see chart).

Why didn’t Reagan do better in the polls? The answer is simple: Throughout most of the campaign, Americans were not convinced that Reagan had the experience, judgment or temperament to be president of the United States and commander in chief of the armed forces. Carter, for all his flaws and the unhappiness Americans felt toward his presidency, was the relatively safer harbor, the devil voters knew.

A Time/Yankelovich poll in August 1980 asked voters to rate Reagan on a 5-point scale, 1 being very good and 5 very poor, as far as experience in foreign affairs was concerned; 42 percent had him at the poor end, either 4 or 5, compared with only 20 percent ranking him at the good end (1 or 2) of the scale. In October 1980, the Los Angeles Times poll asked voters which candidate best fit the description “He has no experience in foreign affairs.” Reagan garnered 45 percent, with 11 percent for Carter and 27 percent for Independent candidate John Anderson.

It wasn’t just inexperience — a view of Reagan driven in part by his continuing image as an actor. There was also a public belief that Reagan was too extreme and too belligerent, an image skillfully spun by the Carter campaign. In September, Gallup asked voters which candidate was best able to keep the U.S. out of war — Carter bested Reagan by 2-1, 50 percent to 25 percent. When asked in the same survey whether each candidate “takes moderate, middle-of-the-road positions,” 82 percent said the characteristic applied to Carter; only 48 percent said it applied to Reagan.

The dynamic of the 1980 race changed with the one presidential debate on Oct. 28, just one week before the election. In that debate, Reagan — toe-to-toe with the incumbent — held his own, showing that he could do just fine in direct comparison to the president of the United States. Reagan framed the election perfectly for voters poised to go to the polls: Were they better off than they had been four years earlier? And he appeared as a reasonable, intelligent, moderate and sane person, making backfire the suggestions that he was a wild-eyed extremist just dying to get his finger on the nuclear trigger to provoke a High Noon-type confrontation with the Soviet Union. From the debate on, Reagan’s 3-point lead widened to his 9-point-plus landslide popular vote margin over Carter on Election Day.

Of course, the parallels are far from exact. This year, there is no incumbent running. While McCain has some assets that counter the extraordinary anti-Bush sentiment out there, the Arizona Senator is still seen far more as the candidate of the status quo in a year when Americans do not want a continuation of the status quo. But he is also viewed as a safe harbor, a man long on the national stage with enough experience at home and abroad to qualify as president.

Obama is not there yet. In June 2008, Pew asked Americans to rate the two candidates on a number of characteristics. On “would use good judgment in a crisis,” McCain beat Obama 47 percent to 38 percent; on “personally qualified to be president,” it was McCain by a whopping 55 percent to 27 percent. In a July CBS/New York Times survey, McCain beat Obama 63 percent to 26 percent on “has better knowledge of world affairs.” And a mid-July NBC/Wall Street Journal poll had McCain over Obama 53 percent to 19 percent on which candidate was better at “being knowledgeable and experienced enough to handle the presidency.”

That gap suggests that Obama, like Reagan, will be unable to widen his lead significantly unless and until voters judge him as crossing the bar of acceptability as a president — but the underlying terrain of the electorate and the election suggests that voters will move to him in sizable numbers if and when he does.

In 1980, Reagan did not cross that bar until the one debate with the two main candidates very late in the game. This year, Obama’s best chance will come when the public focuses en masse on the two candidates in the three debates, beginning Sept. 26 and ending on Oct. 15, three weeks before the election.

Of course, caveats are in order. Events can intercede to change the election’s terrain, as the Russian incursion into Georgia makes clear. McCain’s campaign might be able to continue to sow doubts about Obama’s suitability and capability for the office. And Obama may not acquit himself well in those debates. But if he does, we can expect the narrow margin to begin to widen around the time the World Series opens on Oct. 22.

Norman Ornstein is a resident scholar at the American Enterprise Institute.