With just over eight weeks left until Election Day, the two sides are settling into a set of state-by-state face-offs, with an increased focus on turning out supporters and tough decisions looming about where to invest time and advertising money.

After the stunning announcement by Senator John McCain on Friday that he had chosen 44-year-old Alaskan Governor Sarah Palin as his running-mate, new information emerged over allegations that Ms. Palin tried to use her gubernatorial office to take revenge on her former brother-in-law.

Democrats arriving here said they remained confident that Senator Obama would leave Denver at the end of the week in a strong position to defeat Senator McCain. But a convention that the Democrats had once anticipated would be a breezy celebration of Mr. Obama has turned into a more sober and consequential event.

In 2004, Harold Simmons donated $2 million to the Swift Boat Veterans for Truth, whose advertisements against then-Democratic presidential candidate John Kerry included one that, with allegations since discredited, impugned Senator Kerry’s military service as a Swift boat captain during the Vietnam War.

In its timing, authorship and style of reporting, the book, “Obama Nation: Leftist Politics and the Cult of Personality,” is strikingly reminiscent of the one Mr. Corsi wrote with John O’Neill about Senator John Kerry, “Unfit for Command,” which included various accusations that were ultimately undermined by news reports pointing out the contradictions.

In his statement Friday, the former senator and vice presidential candidate emphasized that his wife, who became a hugely sympathetic figure when she announced that she had breast cancer, had been aware of the affair since 2006.

Although Mr. Obama has been under an intense public spotlight for the last year, he is still relatively new on the national scene, and polls indicate that for all the enthusiasm he has generated among his supporters, many voters still have questions about him.