The race to select a Republican presidential candidate looks certain to get nastier as the stakes get higher, with a new AP-GFK poll showing President Barack Obama becoming increasingly vulnerable.
A strong Republican nominee would be seen as having a reasonable chance of defeating Obama. The AP-GfK poll released Wednesday indicates that half of all Americans now believe Obama does not deserve to be re-elected.
But none of the Republicans vying to challenge him in 2012 has yet been able to outpoll him in a hypothetical head-to-head match up. And the Republican race remains in flux.
Among all adults surveyed, half said Obama should not be re-elected, and 46 percent said he should be. That continues his gradual slide since May.
Yet when all adults are asked about hypothetical head-to-head matchups, Obama and Romney run almost even, with Obama leading 48 to 45 percent. Obama holds a narrow edge over Cain, 49 percent to 43 percent. He leads Perry, 51 percent to 42 percent.
The poll found shifts in candidates' favorability ratings. These numbers don't necessarily track people's likelihood to vote for or against someone, but they offer insight into how candidates are being received as they become better known.
Romney, Cain and former House Speaker Newt Gingrich have gotten positive bumps since August. Romney and Cain are the only Republican contenders viewed favorably by more than 40 percent of all adults.
Romney's favorable rating has risen 10 points among all adults since August, and now stands at 49 percent. Increases came across party lines, but especially among conservative Republicans.
Cain's favorability rating among Republicans has nearly doubled as he has spent more time in the spotlight, increasing from 37 percent favorable in August to 71 percent favorable now. Just 10 percent of Republicans hold a negative impression of him. Party insiders will watch for signs that Tuesday's hard-hitting debate might wound Cain a bit.
Obama's favorability ratings are essentially unchanged since August, with 54 percent of adults holding a favorable view of him, and 44 percent unfavorable.
On Wednesday, Obama teamed up with his popular and personable wife on the final leg of a three-day bus trip, seeking to use her broad appeal to rally support. Michelle Obama's appearance on her husband's driving tour through North Carolina and Virginia, two politically important Southern states, comes as she takes a more active role in the 2012 campaign.
Mitt Romney, the choice of 30 percent of Republicans in the latest poll, is reasonably popular but has yet to pull away from the field. He is plagued by doubts over his conservative credentials, links to Wall Street and the health care law he implemented in Massachusetts that was in part the model for Obama's federal law, widely loathed by Republicans.
Romney is also a Mormon, something that bothers many evangelical Christians who make up a large part of the Republican Party's base.
Increasingly on the defensive, Romney is being hammered on old issues — like an accusation of hiring illegal immigrants to work on his lawn.
Cain earned 26 percent in the poll. Rivals attacked him Tuesday over his catchy "9-9-9" plan that would revamp the U.S. tax code. Rivals said it would raise taxes on most Americans.
The poll, taken before Tuesday's GOP debate, found many are reluctant to back a man who has never held office.
Of the Republicans polled, about four in 10 say they're less inclined to vote for someone who has never been elected to public office. That's far more than say they are disinclined to vote for a Mormon, a woman or a black candidate — another hurdle faced by Cain, who is African American.
Americans have no recent history of electing inexperienced politicians as president except war hero Dwight Eisenhower in the 1950s.
Perry had enjoyed a bump in the polls after his late entry into the race but now lags with only 13 percent. He has recently gone on the offensive against Romney trying to recover lost ground.
The economy is expected to be the biggest issue in the presidential race and Obama's biggest vulnerability.
Republican strategist Alex Castellanos said in a Twitter message after Tuesday's debate, the most acrimonious GOP debate of the year: "All the (Republican) candidates have lost their virginity now. Everybody attacks everybody from now on."
Associated Press writers Kasie Hunt, Philip Elliot, Charles Babington, Jennifer Agiesta, Nancy Benac, Julie Pace and Stacy Anderson and News Survey Specialist Dennis Junius contributed to this report.