Buoyed by a series of strong debate performances, Mitt Romney is suddenly attracting new support from major donors and elected officials, some of whom had resisted his previous entreaties, as people across the GOP grow more accepting of the presidential contender as the party’s standard-bearer.

“He’s viewed as an almost inevitable candidate,” said longtime strategist Ed Rollins, who until last month managed the campaign of Rep. Michele Bachmann (Minn.), one of Romney’s opponents. “He’s the heavy favorite.”

The party establishment seems to be moving Romney’s way, even as a new national poll highlighted the volatility of the race. A Wall Street Journal-NBC News poll showed the surging businessman Herman Cain numerically ahead of Romney for the first time, 27 percent to 23 percent, with Texas Gov. Rick Perry third, at 16 percent.

On Wednesday, Sen. Thad Cochran (R-Miss.) and former House speaker J. Dennis Hastert (R-Ill.) became the latest in a string of current and former elected officials who have announced their support for Romney over the past week. Former Republican National Committee chairman Jim Nicholson, hedge fund manager Paul Singer and Home Depot co-founder Ken Langone are among the major Republican fundraisers supporting the candidate.

“It’s all coming together for him,” said Cochran, who formally endorsed Romney on Wednesday. “People are beginning to be impressed with him and his thoughtful comments about the issues.”

The shift is being noticed not just among Republicans, but Democrats as well. In Chicago, President Obama’s campaign advisers increasingly view Romney as the most likely general-election foe, and on Wednesday they attacked the former Massachusetts governor as taking “diametrically opposite positions” on key issues during his political career.

With three months until primary voting begins, Romney and his political team are hoping to create an increasingly narrow path for his opponents by consolidating as much of the GOP around his candidacy as possible.

Still, considerable obstacles stand in Romney’s way to the nomination, namely winning over social conservatives and tea party activists who have been uneasy with the health-care overhaul he championed as governor of Massachusetts, as well as his shifting positions on abortion and same-sex marriage.

An NBC News-Marist poll released Tuesday found that Romney trailed Cain by 16 percentage points (31 percent to 15 percent ) among Republicans in Iowa who consider themselves supporters of the tea party movement.

Perry, considered Romney’s most durable rival, is trying to exploit those weaknesses and may soon open a new front in the nomination battle. After raising $17 million in the last fundraising quarter, Perry has the money to run commercials attacking Romney in all the early-voting states.

“Romney has done well to sort of regain the front-runner status, but I believe Governor Perry is going to be the alternative — the authentic conservative,” said Henry Barbour, a Perry backer and Republican National Committee member from Mississippi. “And the conservative candidate usually wins in Republican primaries.”

Perry has been dropping in the polls, losing ground to the surging Cain. And in a sign that Romney thinks he has already vanquished Perry, he shifted his campaign message this week away from attacks on Perry’s immigration and Social Security record and toward Obama, stressing populist appeals to the middle class that he could carry into a general election.

Meanwhile, Obama’s top political strategist, David Axelrod, organized a conference call with reporters Wednesday to criticize Romney as taking conflicting positions on health care, taxes and Chinese currency ma­nipu­la­tion.

“Across the political spectrum, people have the same question: If you are willing to change positions on fundamental issues of principle, how can we know what you will do as president? How can we trust who you are?” Axelrod said.

Even as Romney touted new endorsements, he has made clear that he is taking nothing for granted. “I’m not sure I’m the nominee yet,” he quipped in Tuesday night’s Washington Post-Bloomberg debate, after being asked whom he would nominate to chair the Federal Reserve.

“Anybody who gets caught up in the inevitability thing is making a huge mistake,” said a senior Romney adviser, who spoke on the condition of anonymity to discuss campaign strategy. “In Iowa and New Hampshire, you have to earn it, and the minute you think you don’t, you will lose it.”

Romney’s wife, Ann, carried this message Wednesday to Martha’s Exchange here on Nashua’s Main Street, telling a women’s luncheon: “We all know that Mitt’s doing well here, but we don’t take that for granted. We know how hard you have to work for every vote in this state.”

Her eyes misting and her voice cracking, Ann Romney offered an emotional testimonial of how her husband stuck by her side when she found out she had multiple sclerosis. Then she touted his economic know-how.

“I think more and more people are figuring out that Mitt is the one that knows what he’s talking about, that understands not just our economy but world economies, and understands and has the intellectual capacity to be able to deal with a lot of different situations,” she said.

Cochran said the former governor’s steady hand is what so many people have found impressive. “Mitt Romney is running the kind of campaign in a deliberate, careful, professional way that builds a sense of confidence by the American people that he could serve very ably as our president.”

A series of factors have shifted the race decidedly in Romney’s favor. Perry’s fall and Cain’s rise seem to be splintering the votes of conservatives who don’t like Romney, raising the prospect of Romney winning by plurality in such early-voting states as Iowa and South Carolina.

What’s more, the decision of New Jersey Gov. Chris Christie — who would have posed a serious threat — not to run and then to endorse Romney “pulled the cork,” in the words of one Romney adviser, on a bevy of major Republican donors who had been sitting on the sidelines. The new “bundlers,” working to curry favor with Romney, are filling the candidate’s October and November calendar with fundraising events in Florida, New York and elsewhere.

In an interview, Iowa Gov. Terry Branstad, who has not endorsed a candidate, said Romney called him on Wednesday. He said the Christie endorsement could help Romney in the Hawkeye State.

“That definitely will cause some people to give Romney another look,” Branstad said.

One top party strategist, who has deep roots among social conservatives, said that grass-roots activists who have been cool to Romney are realizing that he may be the party’s best pick to face Obama.

“I think there’s a growing realization among the party regulars and the consultant and donor class that borders on almost inevitability,” said the strategist, who spoke on the condition of anonymity to discuss the race candidly.

But other Republicans cautioned that although Romney has more sustained momentum than any other candidate, this has been an unusually fluid race and more surprises could be in store.

“We’re in the Cinderella cycle of the primaries,” longtime strategist Ed Rogers said. “At any given time, somebody’s holding the slipper and trying to put it on. It pops off and somebody else catches it, and they have it for a while. Right now, Romney’s got the slipper.”

Bacon reported from Washington. Staff writer David Nakamura in Washington contributed to this report.

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