WASHINGTON -- Heading into the 2008 presidential race, many Republicans thought Sen. John McCain's image as a deal-making maverick made him the one Republican who might win in an anti-GOP year. His defeat now has observers wondering what might have been had he stuck to his persona.

Instead, the Arizona senator ran a more traditional campaign, appealing to conservative voters who make up the base of his party. His advisers offer a variety of reasons for why he chose this tack, but the decision confounds those who missed the...