No Democratic presidential candidate has won Virginia since Lyndon B. Johnson in 1964, and the selection of Sarah Palin has improved Mr. McCain’s chances of carrying the state. Even so, Senator Barack Obama, the Democratic presidential nominee, still clearly sees an opportunity here, and has opened more than 41 offices in the state.

Despite an intense effort to distance himself from the way his party has done business in Washington, Senator John McCain is seen by voters as far less likely to bring change to Washington than Senator Barack Obama. He is widely viewed as a “typical Republican” who would continue or expand President Bush’s policies.

With economic conditions worsening over the course of this year and voter anxiety on the rise, Senator McCain has had to labor to get past the impression — fostered by his own admissions that the subject is not his strongest suit — that he lacks the experience and understanding to address the nation’s economic woes.

Senator Obama originally built his campaign on his opposition to the Iraq war, but his message has shifted to the economy. The question remains whether Mr. Obama can define his candidacy around the economy, as other Democrats have done, and be seen as connecting with the struggles of Americans.

Once a reliable Democratic voting bloc, Catholics have emerged as a pivotal swing vote in recent presidential races. Evenly divided in a poll over the summer, Catholics make up about a quarter of the national electorate and about a third in the pivotal battleground states of Michigan, Missouri, Ohio and Pennsylvania.

As the Republican vice-presidential nominee, Sarah Palin points to her management experience while deriding her Democratic rivals. But an examination of her swift rise and record as mayor of Wasilla and then governor finds that her visceral style and penchant for attacking critics contrasts with her carefully crafted public image.

Women have voted in greater proportions than men for almost three decades. But the hard-fought candidacy of Hillary Rodham Clinton and John McCain’s selection of Sarah Palin as the first woman on a Republican presidential ticket have put new cultural and ideological elements more fully into play.

Senator Obama is the first presidential candidate to shun public financing, confident that he can keep reeling in small and large donations from his army of givers, which now numbers more than 2.5 million people. Obama has more than $US77 million in cash on hand, according to aides, and will seek to press home his advantage.

Senator Obama knew what he was getting when he picked Senator Biden: A veteran of six terms in the Senate, chairman of the Foreign Relations Committee, an Irish Catholic with working-class roots, a guy who had twice been tested in the arena of presidential politics. And a human verbal wrecking crew.

Senator John McCain’s choice of Gov. Sarah Palin of Alaska as his running mate and the resulting jolt of energy among Republican voters appear to have caught Senator Barack Obama and his advisers by surprise and added to concern that the Obama campaign was not pushing back hard enough against Republican attacks.