WASHINGTON (AP) _ 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.