Obama is expected to keep a low profile this week. Although this week he told reporters to expect a news conference the day after the election, aides said afterward that it would probably happen later in the week.
But Obama was already beginning the transition from presidential-hopeful to president-elect.
On Tuesday night, the senator began the delicate process of trying to win over those who did not vote for him, calling for a renewal of the American spirit in a direct appeal to McCain supporters.
"I may not have won your vote tonight, but I hear your voices," Obama said. "I need your help and I will be your president, too."
The presidency was far from the only office at stake Tuesday. In House and Senate elections, Democrats extended their hold on Congress:
In North Carolina, Democratic state Sen. Kay Hagan ousted Republican Sen. Elizabeth Dole while in New Hampshire, former Gov. Jeanne Shaheen, a Democrat, beat Sen. John Sununu. Democrats also captured seats held by retiring GOP senators in Virginia, New Mexico and Colorado.
The race in Minnesota between incumbent Republican Norm Coleman and former comedian Democrat Al Franken was deemed to close to call. A recount appeared likely.
Races remained without clear winners early Wednesday in Oregon, Alaska and Georgia.
Despite the Senate pickups, Democrats will fall short of the 60 votes needed to prevent a Republican filibuster.
Senate Majority Leader Harry Reid of Nevada credited the excitement and record turnout that helped propel president-elect Obama to victory.
"Obama ran a terrific campaign, he inspired millions of people," Reid said. "It's been a really good night."
In the House, Democrats captured GOP-held seats in the Northeast, South and West, adding at least 17 seats to the 30 they took from Republicans in 2006. Fewer than 10 races remained undecided. Going into Tuesday's election, Democrats controlled the House 235-199 with one vacancy. It is the first time in more than 75 years that the party received larger congressional margins in back-to-back elections.
"Tonight, the American people have called for a new direction. They have called for change in America," House Speaker Nancy Pelosi said.
Republicans encountered early trouble in Florida, where Rep. Tom Feeney — under fire for ties to disgraced lobbyist Jack Abramoff — was the first to fall at the hands of former state Rep. Suzanne Kosmas. Rep. Ric Keller of Florida lost to his Democratic challenger, attorney Alan Grayson.
Republicans also surrendered their last House seat in New England when Democrat Jim Himes, a Greenwich businessman, defeated 22-year veteran Rep. Chris Shays in a wealthy southwestern Connecticut district that heavily favored Obama.
Eleven incumbents held their seats, including governors in Indiana, Montana, New Hampshire, North Dakota, Utah, Vermont, Washington and West Virginia.
Jay Nixon, a Democrat, won a seat in the Missouri's open race that was previously held by a Republican. Jack Markell won Delaware's open race, keeping the position in the hands of Democrats. In North Carolina, Lt. Gov. Beverly Perdue won an open race against Charlotte Mayor Pat McCrory.
In Washington state, Democratic Gov. Chris Gregoire defeated GOP challenger Dino Rossi, a former state senator, in a rematch of a hotly contested 2004 race.