In a sad development, Obama's grandmother, Madelyn Dunham, died of cancer on Monday in Hawaii. Obama had gone to visit her last month. "She was the cornerstone of our family, and a woman of extraordinary accomplishment, strength, and humility," he said in a statement.

The two-year campaign, which has been estimated to cost $2 billion, will extend even into Election Day. McCain will make stops in Colorado and New Mexico after voting in Arizona.

Obama will make a final plea for votes on Tuesday in Indianapolis. Usually a solid Republican state, Indiana is flirting with Obama this year.

Americans will vote in what amounts to 51 separate elections in each state and the District of Columbia. Each state is allocated electoral votes based on the size of its representation in Congress. Whoever gets 270 electoral votes wins the White House.

While Obama has many combinations of states that he can use to get to 270, McCain's path is narrow. He has been mostly racing around states Bush won in 2004 trying to defend them while hoping to nab traditionally Democratic Pennsylvania.

Karl Rove, the Republican strategist who masterminded Bush's election victories, said on his website that based on his review of the polls, Obama could win with 338 electoral votes to 200 for McCain, the largest electoral margin since 1996.

In Congressional elections on Tuesday, Democrats appeared poised to make gains in their majorities in both the US House of Representatives and the Senate. All 435 House seats are at stake and 35 of the Senate's 100 seats are up for election.