Obama shooting for every delegate he can get

CHICAGO -- In the run-up to the biggest primary day of the presidential race, Sen. Barack Obama is campaigning on a large scale.

He flies from city to city, speaking to cheering crowds. He sends out his biggest celebrity endorsers and then surprises voters with another celebrity nod. He bought an ad to air in Feb. 5 states during one of the most-watched television events of the year, the Super Bowl.

But his task Tuesday, when 22 states hold primaries and caucuses, is to win on the smallest scale: hunting delegates one congressional district at a time.

Democrats award delegates based on the percentage of votes candidates receive in congressional districts across the country. As a result, placing second can still earn a candidate delegates.

On Tuesday, 1,681 delegates will be awarded of the 2,025 necessary to win the Democratic nomination.

So even though Sen. Hillary Rodham Clinton is expected to win in her home state of New York, where she leads in pre-primary polls by double digits, Obama's campaign believes he can rack up big wins in largely African-American congressional districts and earn delegates as a result.

"This is a delegate race. That is how this nomination is going to be determined," Obama spokesman Robert Gibbs said. Even if delegate math seems awfully old-style politics for a "change" candidate, he said, "It's the way they pick the nominee, and you've got to play by the rules."

It's also a race to get the attention of as many voters as possible in a short period of time.

Since Thursday's debate, the Illinois senator has campaigned in nine states that vote Feb. 5. The biggest event of the weekend was a Los Angeles rally with Oprah Winfrey, Caroline Kennedy and Obama's wife, Michelle. The event was designed to attract female voters who, according to polls, have so far favored Clinton.

The event featured a surprise endorsement from Maria Shriver, another Kennedy family member. Her husband, California Gov. Arnold Schwarzenegger, endorsed Republican presidential candidate Sen. John McCain last week.