Six national polls, all taken since June 15, show Barack Obama leading John McCain. Two of the surveys indicate that the Democrat is holding a double-digit lead over the Republican: 15 percentage points in the Newsweek poll, 12 points in the Los Angeles Times/Bloomberg News poll. The average: an 8-point lead for Obama.

So, is the presidential contest essentially over? Can we rely on polls taken four months before the election to tell us what is going to happen in November?

A review of Gallup polls taken in June during t he past 14 presidential campaigns--going back to 1952--shows that early polls tend to be reasonably reliable. In 10 of those races, the June polls actually forecast the election result.

In 2004, for example, the June Gallup poll had George W. Bush leading John Kerry by 1 point. Bush ended up beating Kerry by 3. Likewise, in June 1996, Bill Clinton led Bob Dole by 16 points. Clinton ended up winning by 8. In June 1980, Ronald Reagan was leading Jimmy Carter by 1 point. Reagan did end up winning--by 10.

The 1992 contest was unusual because three candidates were running--George H.W. Bush, Clinton, and independent Ross Perot. In June 1992, the three were nearly tied, with Bush at 33 percent, Perot at 32, and Clinton at 27. Clinton was running third! Yet he ended up winning by 6 points.

So was the June poll wildly off? Not really. It was fairly close to the final vote for Bush, the incumbent. (He got 37 percent of the vote.)

In June, the anti-Bush vote was split between Clinton and Perot. In July, Perot withdrew from the race, and Clinton pulled ahead of Bush. Clinton remained ahead for the rest of the campaign, even after Perot got back in on October 1.

What about the four elections that the June polls got wrong? You can see a pattern there, too.

In June 1960, John F. Kennedy was 10 points ahead of Richard Nixon. The November vote turned out to be much closer. Kennedy won by less than half a percentage point. Why was 1960 so close? Because President Eisenhower, the Republican incumbent, was very popular: His job approval was 59 percent. Eisenhower's popularity helped his vice president nearly overtake the Democrat.

In June 1976, Carter was 18 points ahead of Gerald Ford. Carter ended up narrowly beating Ford, the incumbent, whose job-approval rating was close to 50 percent. In June 2000, George W. Bush was leading Al Gore by double digits. The election ended up with Bush winning the electoral vote and Gore winning the popular vote by 0.5 percentage points.

What turned things around for Gore? President Clinton, whose job-approval rating was 57 percent at the time of the election.

The most famous exception was 1988. In June, Michael Dukakis was leading George H.W. Bush by 14 points. Game over? Not quite. Bush ended up defeating Dukakis by 7 points.

The conventional wisdom is that Dukakis lost because the Republicans ran a tough negative campaign that discredited him. But there was something else. President Reagan had a 51 percent job-approval rating, and his popularity helped carry his vice president to victory.

The lesson: Don't just watch the polls; watch the president's job ratings.

That's more bad news for McCain. The latest Gallup/USA Today poll gives President Bush a 28 percent job-approval rating. That's worse than bad. It's just about the lowest job rating ever recorded.

Is there any hope for McCain? Maybe. He is not the incumbent, nor is he the incumbent's vice president. The Republican's message has to be "I'm not Bush!"

"This is, indeed, a change election," McCain said on June 3. "No matter who wins this election, the direction of this country is going to change dramatically."

Obama responded on June 5: "He says he's about change. Everybody's about change these days. But you know what? It's not change when you vote with George Bush 95 percent of the time, as he did last year."

One thing is clear: If McCain intends to prove this June's polls wrong, he certainly can't bank on President Bush's rating carrying him across the finish line.

This article appeared in the Saturday, July 5, 2008 edition of National Journal.

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