WASHINGTON -- Sen. Barack Obama has opened up a double-digit lead in the presidential race, with a growing number of voters saying they're now comfortable with the Democratic nominee's values, background and ability to serve as commander in chief, according to a new Wall Street Journal/NBC News poll.

For months, the race has rested largely on the question of whether voters could get comfortable with Sen. Obama, the first African-American to run on a major party ticket, and one who has been on the national political scene for...