WASHINGTON — The John McCain-Barack Obama election looks like one of the clearest choices in years, but history also shows that presidential contests rarely unfold along logical paths.
The competition at first glance is a quick study in contrasts.
McCain is 71, a Vietnam War veteran who's trying to become the oldest person ever elected to a first term.
Obama's 46, a native of Hawaii and a one-time Chicago community organizer who's trying to become the first black person to win the White House.
McCain is a usually loyal Republican with an independent streak; he's voted with his party 88.3 percent of the time in the current Congress, well above his Republican colleagues' average. He likes the idea of making President Bush's tax cuts permanent and thinks that the Iraq war remains a vital U.S. interest and a noble cause.
Obama is a fiercely loyal Democrat with his own independent thoughts. He's voted with his party 96.4 percent of the time since January 2007. He regards the Iraq war as a tragic mistake and wants to cut taxes for the middle and poorer classes while raising them on the wealthy.
McCain is a 25-year veteran of Congress. Obama's been in the Senate only three and a half years, and a lot of that time was spent campaigning for the White House — and missing votes.
Both candidates face problems, some obvious, some historic.
Both still need to unify their parties. Obama lost most of the year's big battleground states in Democratic contests and did poorly among older white voters, many of whom have said they'll give McCain a look.
McCain, though, still isn't the darling of his party's conservative wing; long after his major rivals left the race, he rarely got more than 75 percent of the Republican primary votes in late spring primaries.
Both also are fighting history, which shows that November voters don't simply go down checklists and contrast candidates' stands on policy questions. Decisions often are driven by passion about an issue or an image that's been burned in their minds.
Three passions seem to be dominant so far this year, and all offer advantages to Obama: ending the Iraq war, restoring a sense of economic security and ousting the Republican Party from the White House.
The war's approval rating was 30 percent in the latest CNN/Opinion Research Corporation poll. Bush's job approval was 28 percent. Economic anxiety is higher than at any time since 1991, and $4 a gallon gasoline isn't helping.
Obama will pound home the idea that "a vote for McCain will be seen as a public acceptance of the idea we can stay there (in Iraq) awhile," said John Fortier, a political analyst at Washington's American Enterprise Institute, a center-right research center.
"The war was his launching pad during the primaries," said Carl Pinkele, a professor of politics and government at Ohio Wesleyan University. "It should continue to be a strong asset."
Yet Obama and McCain are close in most national polls. Gallup's daily tracking polls have had them in a virtual tie for the past week.
Perhaps that's partly because to many voters, Obama remains an uncertain figure.
In contrast, "McCain can pull out his record and show where he has clear positions," said Julian Zelizer, a professor of history and public affairs at Princeton University.
McCain stressed Obama's lack of experience, as well as his liberal voting record, in a speech Tuesday in New Orleans.
"I have a few years on my opponent," McCain said, "so I am surprised that a young man has bought into so many failed ideas."
Among them: "He seems to think government is the answer to every problem."
"Republicans think it will be easy to paint Obama as someone too prone to diplomacy in foreign affairs and taxing and spending in domestic policy. They did that to Mondale and Gore, and it worked," said Zelizer.
Former Vice President Walter Mondale advocated tax increases as a major part of his 1984 campaign, and former Vice President Al Gore in 2000 promised a tax cut only 40 percent as big as opponent George W. Bush's. Both lost.
On the other hand, Obama will say that McCain represents a third Bush term and would push the same radical policies that have led to the Iraq quagmire, the sluggish economy, high oil prices and global disdain for the United States.
Nonsense, McCain said Tuesday.
"I have worked with the president to keep our nation safe," he said, "but he and I have not seen eye to eye on many issues."
Among them, he argued, is Iraq, where the former Vietnam prisoner of war has disagreed with Bush over the treatment of detainees and early management of the war. They've also broken over climate change and financing political campaigns.
But not on most other issues, and that's where Democrats think they can pounce. Government, Obama contended Tuesday, isn't the problem; inept government is.
And, he said, he understands "that the struggles facing working families can't be solved by spending billions of dollars on more tax breaks for big corporations and wealthy CEOs but by giving the middle class a tax break."
And by using federal dollars to improve schools and roads, and protecting Social Security. Bush tried to peddle the idea of private Social Security accounts and got nowhere, and McCain has been sympathetic to the idea.
"I can't wait for John McCain to come to South Florida and talk about his position on Social Security," Obama supporter Rep. Robert Wexler, D-Fla., said sarcastically.
Rep. Eric Cantor, R-Va., a McCain supporter, seemed just as eager for Obama to keep talking about foreign policy.
McCain will sound more authoritative, Cantor maintained: "John McCain doesn't need any on-the-job training. It's in his DNA."