Republican presidential candidate Mitt Romney's drubbing of President Obama at last week's debate in Denver was a game changer for the presidential campaign, new polling confirms.

National tracking polls and surveys of key swing states show Romney leveled the playing field, nipping a once-growing Obama lead and making a GOP victory a far more realistic possibility than it was just a week ago.

In one of the most dramatic shifts, Pew Research reported Monday that Romney not only erased Obama's 8-percentage-point lead in its most recent poll of likely voters but now leads the president by 4 percentage points, a 12-point swing in a matter of days since the debate. Romney now leads Obama 49 percent to 45 percent, according to Pew, which also found that by a 3-to-1 margin voters believe Romney dominated the Oct. 3 debate.

Other polls showed similar, if less dramatic results.

"My polling shows that Obama lost a 4-point lead within 48 hours" of the debate, Ron Faucheux, president of Clarus Research Group, told The Washington Examiner.

Faucheux and other pollsters are now waiting to see if Romney's poll numbers will shift again after the debate Thursday between Vice President Biden and Romney's running mate, Paul Ryan.

For now, though, Romney's breakout debate performance has boosted him in crucial swing states he needs to win if he's going to oust Obama in November.

A Susquehanna Polling and Research survey released Monday showed the race now statistically tied in Pennsylvania. But the poll also found that 76 percent of those surveyed had watched the first presidential debate and 2 percent of them said they had actually switched their support from Obama to Romney based on their debate performances.

The polling data are "clear evidence the debates have helped solidify the Keystone State as a tossup election in November and one well within Romney's reach," said Susquehanna President Jim Lee.

Polls taken since the Oct. 3 debate show the race virtually tied in the swing states of Virginia, Colorado and Florida. And Romney has nearly completely erased Obama's lead in Ohio, a state Romney must win if he's going to win the White House, new polls show.

One of the largest shifts nationally in the race was recorded by Gallup, which found in a poll released Monday that Obama lost 5 percentage points among registered voters since the debate, and is now tied with Romney at 47 percent.

Close to 70 million people watched Obama and Romney debate for the first time, and 72 percent of those polled by Gallup rated Romney the winner, compared with just 20 percent who thought Obama did the better job. Even Democrats thought Romney did better, giving him a 10-point margin over Obama. Romney's overall margin of victory was the largest ever recorded by Gallup, the firm reported.

"The debate appears to have affected voters to some degree, given the narrowing of the race in the three days after the debate compared with the three days prior," Gallup reported Monday.

A second poll released by Gallup showed Obama up by 5 percentage points after a new jobs report was released Friday showing the unemployment rate dropping below 8 percent.

Romney's wife, Ann, told WTOP-FM on Monday that the debate offered voters "a completely unfiltered view" of her husband that ran counter to the barrage of negative campaign ads put on by the Obama administration.