In eight days, on Feb. 5, Obama and his principal rival, New York Sen. Hillary Rodham Clinton, face off in the contest dubbed Super Tuesday, the biggest day of presidential primary voting in U.S. history. Twenty-two states hold Democratic primaries or caucuses that day, spanning political terrain from California to Massachusetts, from Latino communities in the West to majority-black cities in the East, a mix of states that includes some of the nation's most expensive television advertising markets.
Super Tuesday is a particular challenge for Obama, who trails Clinton in most national polls. Three of the biggest states voting -- New York, New Jersey and Connecticut -- are in Clinton's backyard; a fourth, Arkansas, was her home before her husband was elected president. Those states account for one-quarter of the delegates to be awarded that day.
In California, which holds the biggest cache of delegates, polls show Clinton has a commanding -- although narrowed -- lead over Obama.
Moreover, the multi-state field of Super Tuesday does not play to Obama's signature strength: his ability to win over voters in live town-hall settings, using his soaring oratory and personal charm. That worked for him in Iowa, where many voters met him personally more than once. In a national campaign, by contrast, most voters' only contact with Obama will be through advertising and surrogates.
Still, the Obama campaign has a strategy for countering Clinton's big-state advantage -- one built in part on the Democratic rules for how delegates are awarded.
Rather than a winner-take-all system, in which the candidate who gets the most votes in a state claims all the delegates, Democrats have elaborate rules that award delegates in proportion to each candidate's share of the vote.
That means even a Clinton stronghold like New Jersey may produce some delegates for Obama -- and it explains why Obama visited Jersey City this month, weeks before New Jersey was set to vote, where a crowd of about 4,500 lined up to hear him.
Despite early predictions that the primary contest would be resolved by Feb. 5, both the Clinton and Obama campaigns now assume that neither candidate will lock up the nomination that day. Even a Clinton strategist predicts that the two will emerge with very close delegate counts.
In all, nearly 1,700 delegates will be awarded on Super Tuesday, a big boost toward the 2,025 needed to clinch the Democratic nomination. California will award 370 delegates that day, or about 22% of the delegates at stake. Republicans will hold their own nominating contests Feb. 5, most in the states where Democrats are voting.
The last two days have strengthened Obama's hand.
His 28-point victory margin over Clinton on Saturday in South Carolina was far wider than most predicted, giving Obama energy and new funds. His campaign raised $500,000 through its website in the hour after the South Carolina polls closed, according to a spokesman. Obama carried 55% of the vote in South Carolina, compared to 27% for Clinton and 18% for John Edwards.
On his way to winning South Carolina, Obama drew support from about 80% of African American voters, exit polls showed. That leaves him positioned to do well Feb. 5 in states such as Georgia, Alabama and Tennessee, which have large populations of African American Democrats.
The biggest prize among these states will be Georgia, where blacks could make up more than 40% of the Democratic primary vote, and 87 delegates are at stake. Obama has been endorsed by Atlanta's black mayor, Shirley Franklin, and recent polls show he has an edge over Clinton in the state.
Obama argued Sunday that his South Carolina victory, in which he won about a quarter of white voters, showed that he appeals to all races. While some think that "if you get black votes, you can't get white votes," his success in South Carolina proved that untrue, Obama told a crowd of more than 9,000 at the University of Alabama at Birmingham.
Kennedy, the Massachusetts senator and one of the Democratic Party's most senior figures, will campaign for Obama and help him shore up support among Latino voters, said someone close to the endorsement announcement.
Latino voters are a mainstay of Clinton's base, and they have a large presence in California, Arizona and several other states that vote Feb. 5. The Obama campaign believes that Kennedy will carry influence among Latinos in part because of his prominent role in calling for an overhaul of immigration laws that includes a path to citizenship for undocumented workers.
Kennedy is expected to endorse Obama at a rally at American University in Washington. News of Kennedy's decision came the day that his niece, Caroline, backed Obama in a New York Times opinion article in which she said Obama could inspire Americans as did her father, President Kennedy. Caroline Kennedy is scheduled to appear at today's rally as well.
Obama already had a leg up on the third-largest delegate prize of Super Tuesday: his home state of Illinois. And he has built organizations in the six states that are holding caucuses rather than primaries: Alaska, North Dakota, Colorado, Minnesota, Kansas and Idaho. The caucus format, which requires voters to attend meetings to express support for their candidate, plays to the Obama campaign's strength in grass-roots organizing that it honed in the Iowa caucuses.