Barack Obama built a formidable lead in his bid to become the first black president Tuesday night, pushing ahead of John McCain in a nation clamoring for change. Fellow Democrats took four Senate seats from Republicans, and reached for more.

Obama gained precious ground in Pennsylvania, winning the state’s 21 electoral votes and depriving McCain of the Democratic-leaning state where he had tried hardest to break through. Obama also swept through territory typically friendly to Democrats in the East and Midwest.

McCain countered in the safest of Republican states.

That left the battlegrounds to settle the race: Florida, Ohio, Virginia, Colorado and more. Most were customarily Republican, but Obama spent millions hoping to peel away enough to make him the 44th president, and his triumph in Pennsylvania left the Republican with scant room for error.

“May God bless whoever wins tonight,” President Bush told dinner guests at the White House, according to spokeswoman Dana Perino.

A jubilant crowd of thousands gathered in Grant Park in downtown Chicago on an unseasonably mild night, confident it would be Obama. They reacted each time Obama was announced the winner in another state — and the cheers were particularly loud when Pennsylvania fell.

Interviews with voters suggested that almost six in 10 women were backing Obama nationwide, and men leaned his way by a narrow margin. Just over half of whites supported McCain, giving him a slim advantage in a group that Bush carried overwhelmingly in 2004.

The results of The Associated Press survey were based on a preliminary partial sample of nearly 10,000 voters in Election Day polls and in telephone interviews over the past week for early voters.