Americans broadly expect Barack Obama to be a one-term president, even as the Republican contest to challenge him churns wildly.

Rick Perry, slammed by poor debate performances after a soaring start, has lost ground badly – hemorrhaging support from older Americans and very conservative Republicans, and relinquishing the overall advantage in his party’s contest to Mitt Romney. Instead it’s Herman Cain’s turn to surge: He’s suddenly running evenly with Perry in the latest ABC News/Washington Post poll.

New Jersey Gov. Chris Christie, when added to the mix, debuts with 11 percent support in this poll, produced for ABC News by Langer Research Associates. While that means nine in 10 don’t side with the Garden State governor, 42 percent of Republicans and Republican-leaning independents also said they’d like him to run – more than say that about the other major figure still in the wings, Sarah Palin.

These results signal the unsettled nature of the Republican contest. Among announced candidates, Romney has 25 percent support, unchanged from last month; Perry has 16 percent, down by a steep 13 points; Cain, with 16 percent, is up sharply from 4 percent a month ago.

Best for Cain and Christie alike is the way in which potential Republican voters are warming to them. Forty-seven percent say the more they hear about Cain the more they like him versus 18 percent who like him less. It’s a similar 43 to 23 percent positive for Christie.

Perry is heading in the opposite direction, with more negative reviews than positive ones. His troubles since his lackluster debate performances are unmistakable, and serve as a cautionary sign for those enjoying their moment in the sun. Forty-four percent of Republicans and Republican-leaning-independents now say the more they hear about Perry, the less they like him, outnumbering the 30 percent who like him more. And among those who watched last week’s debate, many more – 63 percent – said they liked Perry less.

Romney gets an even split on this score – like his overall support numbers, he appears to be neither gaining ground nor losing it, which for a frontrunner could be worse. Head-to-head against Perry, Romney leads on experience and electability; the two are close in trust to handle the economy, as well as on Social Security.

CAIN and PERRY – The sharpest changes are between Perry, long-serving governor of Texas, and Cain, a businessman who’s never held elective office. Cain – in the headlines for winning a Florida Republican Party straw poll last week – has moved up among several of the groups in which Perry’s lost ground.

Perry’s lost 36 points in the past month among leaned Republicans who are following the election very closely; Cain’s gained 30 points in this same group. Cain now wins 36 percent support from those paying very close attention, vs. 24 percent for Romney, 12 percent for Perry.

Perry, attacked in the debates for calling Social Security a failure and a Ponzi scheme, has lost 35 points among older Americans. Criticized by conservatives for signing an order mandating a vaccine for pre-teen girls and for offering in-state college tuition to illegal immigrants, he’s lost 35 points among strong supporters of the Tea Party political movement, and 27 points among very conservative Republicans; Cain’s gained 25 and 16 points in these groups, respectively.

Cain also has gained 22 points among Republican-leaning independents. He’s tied with Romney among leaned Republicans who’ve watched the debates, with 27 and 26 percent support, versus 14 percent for Perry. And leaned Republicans who’ve watched the debates said the more they hear about Cain the more they like him by a vast 70 to 12 percent.

OBAMA – Obama, for his part, presiding over the longest and deepest economic downturn since the Great Depression, is down to 42 percent approval for his job performance, numerically a new low, and not the kind of number that lends itself to re-election. He’s at career lows specifically among independents – key swing voters – and moderates.

Fifty-four percent of Americans disapprove of the president’s performance. That includes 40 percent who disapprove strongly, outnumbering strong approvers by 2 to 1.

While the intensity of his critics is trouble for Obama, so are expectations that he won’t be re-elected; Americans by 55-37 percent expect the eventual Republican nominee to win. Such views can inform voter enthusiasm – precisely the ingredient that led the GOP to its broad success in the 2010 midterms. (See separate analysis, released Monday.)

HEAD to HEAD – General-election matchups remain quite close, with support for Obama’s challengers below his disapproval rating, indicating that discontent with the president hasn’t yet coalesced into full-throated support for the other side.

Obama has 47 percent support  versus 46 percent against Romney; this flips to 46 to 48 among registered voters. It’s 46 to 44 percent among all adults for Obama-Christie and 49 to 44 percent pitting Obama against Perry. The differences are not statistically significant.

In these trial heats, Romney and Christie numerically edge out Obama among independents, and come close among moderates. Perry, by contrast, does not have a numerical edge among independents, and trails Obama among moderates by 20 points.

By another measure, 46 percent of Americans said they definitely would not support Obama for re-election, about where it’s been since spring, leaving him fairly little margin for error in his 2012 campaign. Notably, though, nearly as many, 44 percent, flatly rule out Perry; fewer, 37 percent, reject Romney out of hand.

Some differences among groups underscore Romney’s room to navigate. Fewer independents wouldn’t consider Romney, 34 percent, than say that about either Obama or Perry (48 and 46 percent, respectively). And while 85 percent of Republicans say there’s no way they’d support Obama, fewer Democrats, 63 percent, flatly rule out Romney. (It’s similar for Perry among Democrats).

ISSUES – As the president’s likely to point out in the campaign ahead, he’s got potential advantages on some issues, depending on the GOP nominee. Americans by 44 to 21 percent say they’re more apt to support a candidate who sees global warming as a problem to be addressed. And by 42 to 25 percent they’re more apt to oppose one who favors a constitutional amendment banning same-sex marriage.

That said, Americans by 43 to 29 percent also said  they’re more apt to support than oppose a candidate who favors repealing the new health care law, a centerpiece of Obama’s presidency and now a potential liability as he seeks a second term.

On other issues, the public is broadly more likely to oppose a candidate who favors allowing states to opt out of the Social Security system, by 52 to 24 percent, a potential vulnerability for Perry. And by 50 to 18 percent Americans are more likely to oppose a candidate who favors providing in-state tuition for illegal immigrants, a policy of Perry’s in Texas. (Using the word “undocumented” instead of “illegal” doesn’t meaningfully change the result.)

More narrowly, Americans by 35 to 28 percent said  they’re more likely to oppose than to support a candidate who favors teaching creationism or intelligent design alongside evolution as part of the science curriculum in public schools.

Two of these represent challenges for Perry in his own party. Leaning Republicans said  by 41 to 33 percent that they’d be less likely to support a candidate who favors allowing states to replace Social Security with their own retirement systems, a suggestion Perry has characterized as worthy of discussion. And by a broad 63 to 12 percent, they are more likely to oppose a candidate who supports in-state tuition for illegal immigrants; 47 percent are “much” less apt to support such a candidate.

GOP ISSUES and ATTRIBUTES – Issues matter; Republicans and Republican-leaning independents by 73 to 20 percent said  it’s more important to them to support the candidate they agree with the most than the one who’s most likely to win. That’s a relative weakness for Romney; head-to-head against Perry, leaned Republicans by 43-37 percent describe Perry as closer to them on the issues.

At the same time, Romney numerically leads Perry on several issues – 44 to 34 percent in trust to handle the deficit, 44 to 35 percent on the economy and 41 to 34 percent on Social Security and immigration alike. Perry has a numerical advantage, 42 to 35 percent (none of these is statistically significant) over Romney on health care. Romney’s opponents have criticized the mandatory coverage law he signed as governor of Massachusetts.

Of these, the economy, naturally, stands tall. Fifty-one percent of leaning Republicans identify it as the single most important issue in their choice for the GOP candidate for president; the deficit trails distantly, cited by 13 percent, with all other mentions in the single digits. Those most concerned about the economy fracture when asked the next most important issue – two in 10 say taxes; one in 10 apiece mention the deficit, health care and foreign policy issues.

Separately, on personal attributes, Perry paces Romney, 40 to 37 percent, on empathy – who “better understands the problems of people like you.” Still, in having the better experience, it’s Romney by 50 to 30 percent; and in electability it’s similar, 51 to 31 percent for Romney.

WINGS – Christie’s renewed interest – he’d said he would not run, then said he’s reconsidering – garners some support, albeit not a mandate. While, as noted, 42 percent of leaned Republicans would like to see him enter the race, 34 percent would like him to stay out, and 24 percent have no opinion either way.

Christie does best, naturally, among the three in 10 leaned Republicans who are dissatisfied with the current field of candidates. In this group, 22 percent support him for the nomination.

Any way it’s sliced, Christie’s in a better position for a late arrival than is Sarah Palin. Republicans and Republican-leaning independents say by 49 to 35 percent that the more they hear about Palin, the less they like her. And by 2-1, 66 to 31 percent, they’d like her not to enter the race.