The contrasts could not be more stark: an African-American Democrat versus a white Republican. The latter old enough to be the father of the former. One with no military experience, the other with a long Navy career punctuated by a harrowing period of captivity in a Hanoi prison camp. One with a soaring rhetorical style that can light up a sports arena, the other more comfortable in the back-and-forth banter of a town-hall meeting.
Then there are the policy differences between the two presumptive major-party nominees for president. John McCain (R) is one of the Senate's most outspoken supporters of the Iraq war, while Barack Obama (D) has opposed it from the start. Senator McCain wants big tax cuts and less government spending; Senator Obama wants tax breaks targeted at the middle class and greater government involvement in job creation. On healthcare, McCain emphasizes consumer choice and market forces, while Obama favors government action that puts the nation on track toward universal coverage.
As the 2008 general election campaign kicks off, one point is already certain: The outcome will be historic. America will elect either its first African-American president or its oldest first-term president. But just as striking as their differences is a key similarity. Neither was the first choice of their party establishment for the nomination, and both have promised "a different kind of politics" from the highly partisan, divisive wrangling that has come to mark Washington for the past 20 years.
Both men hold appeal among independent voters – about a third of the electorate – and whoever wins a majority of them wins in November. So while both candidates must hold onto the bulk of their party regulars, they will also play to the nonideological center in a way that the nominees didn't in the last two presidential races.
Still, for McCain, the anti-Republican headwind he faces cannot be underestimated.
In any analysis of the 2008 race, "you start with the already-well-described Democratic advantage this time around, beginning with unhappiness over the war and the economy," says Bruce Buchanan, a political scientist at the University of Texas, Austin.
President Bush's abysmal job approval ratings also don't do McCain any favors. Even if Bush were doing reasonably well, history would still point toward a Democrat in 2008. Rarely is a two-term president succeeded by the nominee of his own party.
Generic polls show Americans preferring, with no names attached, a Democratic president to a Republican by a double-digit margin.
But McCain's image of independence and working across the aisle gives him a shot in November. So far, he is holding his own in polls versus Obama.
One of the great unknowns is the race factor. With no historical precedents for a nonwhite nominee, it is impossible to predict how or where Obama's race will affect his chances.
While McCain faced some grumbling among key GOP constituencies when he locked up the party nomination – particularly among movement conservatives and evangelical voters – Obama, too, must unify his party after a divisive primary season. He will need the support of the working class, older, and Hispanic voters that flocked to Hillary Rodham Clinton, and thus how she ends her candidacy and whether she works hard for Obama's election loom large over Obama's chances.
Party strategists warn against making too much of the intraparty squabbling.
"After eight years of George Bush, I just don't think Democrats will be voting for Republicans," says Mr. Carrick. "And when things calm down, they'll recognize that it's in the Democrats' best interest to elect Senator Obama. And Republicans will have the same feeling about McCain."
This leaves the moderates and the independents as the battleground. McCain is already trying mightily to distance himself from Bush, appearing in public with him as little as possible and pointedly criticizing his administration for its blunders, such as the handling of hurricane Katrina and what McCain saw was mishandling of the early years of the Iraq war.
McCain is also seizing opportunities to highlight his policy differences with Bush, such as his support for limits on greenhouse-gas emissions that the Bush administration resisted.
But every time the debate comes back to Iraq, McCain risks looking in lock step with Bush. McCain was a big proponent of last year's "surge" in US troop presence in Iraq, and so his complaints of the handling of the war have diminished.
Going forward, the mantra that Obama introduced first – change – will now be the theme of both campaigns. From the McCain camp, the question will be whose change do voters want, the change that a "maverick," experienced leader can bring, or the change that a young man who just four years ago was a state senator in Illinois can bring.
From the Obama camp, the emphasis will be on judgment over years of Washington experience.
During the primaries, Senator Clinton failed to gain serious traction over her highly debated advertisement asking voters whom they would want answering the phone at 3 a.m. In fact, analysts say, it may have only served to point to McCain as the most experienced candidate on national-security matters.
But even there, as polls show Americans more concerned about the economy than about Iraq or terrorism, McCain starts his general election run with a big anchor around his legs.
"He's in a tough situation, McCain, given that the major issues are going to be economic and that these issues do favor a Democratic candidate," says Stephen Wayne, a political scientist at Georgetown University.
"McCain can campaign if he wants on national-security grounds, but unless there's a change in the international environment and a perceived threat to the US, I don't know where that's going to get him."
McCain's admitted weakness on economic matters could be helped by selecting a running mate with a strong reputation on economics and finance, such as former Rep. Rob Portman (R) of Ohio, also Mr. Bush's former budget director, or Mitt Romney, ex-governor Massachusetts and a wealthy businessman.