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.

Alaska’s economic well-being — sustained by oil and federal spending — has allowed Sarah Palin to avoid some of the tough budgetary choices vexing other governors. That raises questions about how much Ms. Palin’s experience is relevant to the rest of the nation and how much she can relate to struggling blue-collar voters.

At a lunch Friday in Minneapolis, two of John McCain’s top advisers — Charlie Black, a veteran political operative, and Dan Coats, a former senator from Indiana — were extolling Alaska Gov. Sarah Palin’s virtues to about 150 influential evangelicals as evidence of the senator’s ideological commitments.

Even though Senator Biden comes to the Democratic ticket with decades of political relationships and personal history in electoral battleground states that Senator Obama cannot match, the new team’s advisers acknowledge that Mr. Biden is not a cure-all for the political challenges facing Mr. Obama, of Illinois.

Senator Hillary Rodham Clinton of New York ran 40 percentage points ahead of Senator Obama in rural areas of the state during the Democratic primary. With its neighborhoods of white working-class laborers and retirees and fraying party loyalties, it has become a most uncertain political terrain and an inviting target for Senator John McCain — and one that could tip the electoral balance in Pennsylvania, a place packed with electoral votes.

Republican Party’s challenges in the nine-state Northeast region are a reflection of what the party faces across the country as it is being forced to defend dozens of Congressional seats that are now considered competitive at a time when the party has limited financial resources, political analysts said.