COLUMBUS, Ohio (AP) — Barack Obama won the White House on Tuesday, picking up the swing state that decided the presidential election four years ago and winning others that Republicans once considered theirs.

The Democrat defeated John McCain here and built an insurmountable Electoral College win to become the first black president. Obama's Ohio victory denied McCain particularly precious territory; no Republican has ever won the presidency without the state.

Obama picked up Ohio's 20 electoral votes toward the 270-vote threshold needed to earn the White House.

"Senator Obama and I have had and argued our differences, and he has prevailed. No doubt many of those differences remain," McCain said in a concession speech in Phoenix. "These are difficult times for our country. And I pledge to him tonight to do all in my power to help him lead us through the many challenges we face."

Obama and McCain went into Tuesday in close quarters. But with votes counted, it was clear the electorate favored a fresh face and agent of change amid a climate of economic uncertainty.

Ohio narrowly gave President Bush a second term in 2004; he defeated Democrat John Kerry by a 10-vote-per-percinct margin.

But exit poll interviews with Ohio voters on Tuesday found that key swing groups that went for Bush four years ago — independents, moderates, and women — threw their support behind Obama. The Democrat also won across all age groups except those 65 and older.

The exit polls for The Associated Press and television networks also found that six out of 10 Ohio voters said the economy is the most important issue now facing the country.

Obama easily carried the northern half of the state where industrial cities including Toledo, Cleveland and Youngstown have been hit hard by job losses, exit polls found. He also managed to split the vote in reliably Republican southwest Ohio.

Obama won by a wide margin among women voters who four years ago split evenly by the two parties.

A third of the voters cited change as the quality that mattered most, and Obama won among nearly every one of those voters. He also dominated among those worried about the direction of the economy in the next year.

"There was a headwind from the state," McCain adviser Rob Portman told The Associated Press, citing the economic meltdown and a hostile environment for Republicans.

"Sen. McCain had an uphill battle."

That's why both candidates devoted time talking about pocketbook issues with voters. In the end, the conversation turned toward Obama's favor.

Ohio saw its share of activity from both candidates. Obama drew 30,000 to a weekend rally at the Statehouse here. Both party's vice presidents traipsed across the state in recent days. And neither conceded the campaign on television. Combined, they aired $2.7 million in ads during the final week.

Obama had enjoyed a comfortable lead during recent weeks, although polls showed the two were tightening. A final flurry of activity came during the campaign's final days, leaving the race a genuine tossup in its final hours.

More than 666,000 new voters had registered since January, a number that seemed to favor Obama. The Democratic primary in March spurred thousands to register so they could pick between one-time rivals Obama and Sen. Hillary Rodham Clinton. That March 4 primary gave Clinton a 9 percentage point victory and enough momentum to keep her in the race until June.

Obama, however, didn't shut down his Ohio office. Instead, he kept organizing the state as if he had already won. After he finally reached enough delegates, he simply turned on the switch and his massive machine went into motion.

In the final days, some 11,000 Obama volunteers went door to door in Ohio, trying to get out the vote.

McCain and his Republican Party's efforts couldn't keep up.

McCain earned his nomination in March, yet was slow to put in place a campaign in this state. Instead, conservative allies fretted he was wasting a chance to get a jump start. Much of the late spring and early summer, McCain and his allies spent swiping back at conservative activists.

It wasn't until McCain picked Alaska Gov. Sarah Palin as his vice presidential pick did the party's base rally behind McCain, who was often seen as too independent for many Republicans. Palin's choice energized the activists and volunteers, tapping into the grass-roots organizers that gave President Bush a win here four years ago and a second White House term.

"I think it was helpful because she was able to provide us with the additional enthusiasm for the grass-roots effort. Without that, we would've had a tough time with our numbers," said Portman, a former Ohio congressman who ran Bush's budget office until last year.

McCain and Palin — and their supporters — blanketed Ohio during the campaign's final days. Obama's apparent lead in the polls forced them to spend time and money here. In the meantime, they were forced to look away from Virginia, North Carolina and Indiana — all states that were comfortable wins for Bush in 2004 yet were trending in Democrats' favor.