(FORTUNE Magazine) – With the 1996 presidential election season at hand, prognosticators will soon be barraging us with leading indicators that purport to shed light on the eventual results. Here's one most of them overlook: The single most powerful predictor of presidential election outcomes is how smoothly the parties' conventions run.

True, as forums for selecting nominees, today's conventions--unlike those of times past--are meaningless affairs that do little more than rubber-stamp a choice made earlier in primaries and caucuses. But in the television age, the convention has also become an easy way for voters who normally tune out politics to judge the nominees and assess their mettle and the state of their organization. If a party and its candidate don't have their act together, these otherwise empty rallies provide a robust hint to voters that they can't govern. If a putative president can't control his own partisans, the thinking seems to go, how can he control Congress? And if a candidate can't dominate his convention--if he is overshadowed by a pretender to the throne--how can he lead the country?

Still unconvinced? Consider recent history.

1964: Democrats united enthusiastically behind LBJ in Atlantic City. Republicans divided bitterly at the Cow Palace in San Francisco, with Goldwater conservatives booing Rockefeller moderates off the podium and near fistfights on the floor.

1968: "The whole world is watching," chanted antiwar activists as they taunted police and eventually rioted outside the Democratic convention hall in Chicago. Inside, the scene at the most famously divisive convention in modern times was only slightly more civil. In Miami the Republican convention was a sterile but tranquil polar opposite, with Nixon forces adroitly quelling any revolts by potential challengers like Ronald Reagan.

1972: Both parties met in Miami. Democrats remained bitterly divided between party regulars, who backed Hubert Humphrey, and the antiwar reformists, who took over the party and made George McGovern their candidate. Ferocious procedural battles underscored how tenuous the McGovernites' control was, and when their man finally delivered his acceptance speech, it came well after 2:00 a.m. Richard Nixon's convention, by contrast, was ridiculed by reporters for its puerile, upbeat tone. What voters saw, however, was that at least one party's nominee was in firm charge of his team and its affairs.

1976: Only we political junkies now recall it, but the GOP convention in Kansas City was one of the most exciting in modern times-exciting because we couldn't be sure, until the Mississippi delegation tipped its hand, whether incumbent president Gerald Ford or insurgent challenger Ronald Reagan would win the party's nomination. In a more muted echo of 1964, the story was again about a GOP divided between conservatives and moderates, and a candidate who had to struggle to win his own troops' approval. On the Democratic side, Jimmy Carter's convention in New York City was a picture of party unity and tranquillity.

1980: By 1980 the Democrats' unity had dissolved. President Jimmy Carter was dogged throughout the primaries by liberal challenger Ted Kennedy, whose forces triggered bitter fights over platform planks and who himself dominated the convention with a rousing speech that ended with the line--"the work goes on, the cause endures, the hope still lives, the dream shall never die." The speech, which sparked a 35-minute emotion-filled demonstration, completely overshadowed the incumbent president. The contrast with the earlier Republican convention in Detroit, where Republicans united enthusiastically behind Ronald Reagan, was stark.

1984: This was one of the rare times in the past three decades when an incumbent president had an easy road to renomination, and the concomitant ability to orchestrate his convention to a tee. The well-oiled machine behind Ronald Reagan was a sharp contrast with the earlier Democratic convention in San Francisco, where drag queen Sister Boom-Boom and other colorful outsiders vied for TV time with nominee Walter Mondale. Nor could Mondale keep Mario Cuomo from being the dominant force at the convention with his electrifying "City on the Hill" speech.

1988: At Michael Dukakis's nominating convention in Atlanta, the story for the week was...Jesse Jackson. How prominent would Dukakis allow Jackson to be at the convention? How strongly, in the end, would Jackson endorse Dukakis? The answers: Jackson waged an acrimonious floor fight over the platform and used his prime-time slot to ignite his liberal backers and make Dukakis seem tepid and uninspiring by comparison. In New Orleans, despite some furor over George Bush's choice of Dan Quayle as running mate, the GOP convention was skillfully controlled, and the dominant moment was clearly Bush's "thousand points of light; read my lips" acceptance speech.

1992: Bill Clinton's New York City convention was as tightly orchestrated as any Democratic convention since LBJ's in Atlantic City. Dissidents were either suppressed entirely (like Pennsylvania's antiabortion Governor Robert Casey) or relegated to time slots when nobody was watching (like Jerry Brown). Unity was the watchword, and the dominant speech was Clinton's. George Bush's Houston convention, however, was rife with ideological tension, and the most riveting moment by far was the prime-time speech of Pat Buchanan--a right-wing, take-no-prisoners, clarion call equivalent of Ted Kennedy's left-wing speech in 1980. Result: Houston underscored both the deep division in GOP ranks and the weakness of the president.

See a pattern here? Now consider which party in 1996 is likely to have the most fractious, divisive convention: the Republicans in San Diego, fresh from a wild-and-woolly, nine-way (or more), yearlong primary fight and split by deep rifts between "big tent" moderates, Buchananite nativists, and social conservatives? Or the Democrats, who meet two weeks later in Chicago to anoint an incumbent President Clinton, who at this point has no serious challenger and whose White House should be able to firmly control its party's proceedings?

Plenty could change between now and next summer, of course. But if the GOP can't swerve off its current collision course, and if the Democrats can continue to keep from fragmenting, the iron law of convention politics suggests that, come September, Bill Clinton's chances for reelection will look far better than either current polls or the electoral college map now suggest.

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