By PETER WALLSTEN And DANNY YADRON

The tea party has emerged as a potent force in American politics and a center of gravity within the Republican Party, with a large majority of Republicans showing an affinity for the movement that has repeatedly bucked the GOP leadership this year, a new Wall Street Journal/NBC News poll has found.

In the survey, 71% of Republicans described themselves as tea-party supporters, saying they had a favorable image of the movement or hoped tea- party candidates would do well in the Nov. 2 elections.

Already, the tea-party movement has helped to oust a number of incumbents and candidates backed by party leaders in this year’s GOP primaries amid complaints that they lacked commitment to small-government principles. The poll findings suggest that the rising influence of the movement, with its push to cut spending and oppose the Democratic agenda, will drive the GOP to become more conservative and less willing to seek common ground on policy.

“These are essentially conservative Republicans who are very ticked-off people,” said Republican pollster Bill McInturff, who conducted the survey with Democratic pollster Peter Hart.

If the Republicans win control of the House or Senate this fall, Mr. McInturff added, the survey shows “enormous amounts about how limited the interest is going to be in those new majorities to try to seek negotiation with the president or the Democratic leadership.”

The poll found that tea-party supporters make up one-third of the voters most likely to cast ballots in November’s midterm elections. This showed the movement “isn’t a small little segment, but it is a huge part of what’s driving 2010,” Mr. Hart said.

The survey also found growing energy among some core Democratic voting blocs, such as African-Americans and Hispanics—a tightening that is common as an election draws closer, according to pollsters.

The GOP now holds a three-point edge, 46% to 43%, when likely voters are asked which party they would prefer to control Congress. That is down from a nine-point Republican lead a month ago.

Still, Republicans retain major advantages, including a fired-up base. Two-thirds of GOP voters say they are intensely interested in the election, compared with about half of Democrats, suggesting that Republican voters are more likely to turn out at the polls.

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The tea party is a major driver of the so-called enthusiasm gap, with three-quarters of supporters saying they are intensely interested in the election.

President Barack Obama’s ratings remain low, with 46% of Americans approving of his job performance. Half of Americans have a negative view of House Speaker Nancy Pelosi, compared with 22% taking a positive view.

The findings show how the tea-party movement has grown over the past two years from a loose confederation of activist groups into a marquee brand within the GOP that has upended a number of primaries in recent months.

Those include the defeats of incumbent Republican Sens. Robert Bennett in Utah and Lisa Murkowski in Alaska, and the recent victory in Delaware’s Senate GOP primary of Christine O’Donnell, who was backed by some tea-party groups. Ms. O’Donnell upset a liberal Republican, U.S. Rep. Mike Castle, who was aggressively backed by the party establishment.

The survey showed that tea-party supporters are interested in protesting “business as usual” in Washington. The most popular issue motivating them is cutting government spending and debt, followed by reducing the size of government.

Mr. Obama’s health-care overhaul, which sparked unrest last year at congressional town-hall meetings and helped propel the movement to prominence, ranked fourth on the list of issues among tea-party supporters.

Republicans, the survey shows, welcome the change within the party.

“The tea party has to a certain extent scared the Republican Party,” said one poll respondent, Tim Bahmer, a 44-year-old Republican and self-employed auto mechanic from Charlotte, Mich. “From what I’ve seen of what the tea party is saying, I think that could be the change [Republicans] could benefit from.”

Another respondent, Scott Gonzalez, a 33-year-old Republican from Aurora, Ill., said some facets of the tea-party movement might be too conservative for his taste. But, he added, tea-party supporters “tend to be fiscally conservative, which I do like.”

“Hopefully, it will just help both parties understand that people are more or less frustrated and they want to know where politicians are on issues,” he said.

Mr. McInturff said the tea-party movement had not necessarily drawn new people into the GOP. Rather, he said, “a substantial chunk of the Republican Party is rebranding themselves.”

The movement’s greater strength within the party could be significant beyond 2010, as the party looks toward choosing a nominee in 2012 to challenge Mr. Obama.

One beneficiary could be former Alaska Gov. Sarah Palin, who is viewed positively by about two-thirds of tea-party supporters, making her more popular in the movement than other potential presidential candidates included in the new survey.

Slight majorities of tea-party supporters also feel positively about former Arkansas Gov. Mike Huckabee and former House Speaker Newt Gingrich. Just four in 10 feel positively about former Massachusetts Gov. Mitt Romney.

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The movement’s power is emerging as Mr. Obama and top Democrats are trying to mobilize their base and attract independent voters by portraying tea-party-backed candidates as an extreme force within the Republican Party.

The survey suggested that the strategy could have mixed results. More than a third of independents in the survey expressed an affinity for the tea-party movement. Yet 59% of independents said they were not tea-party supporters.

The poll found that the country’s uncertain economy continues to be the overriding issue in the midterm elections.

Seven in 10 adults felt the country remains in recession. And among people who said the recession had a major impact on them and their family, more said they preferred a GOP-controlled Congress to a Democratic-run Congress. One in four adults thought the economy would get worse over the next 12 months. Of that group, two-thirds were people with an affinity for the tea-party movement.

Write to Peter Wallsten at peter.wallsten@wsj.com and Danny Yadronat daniel.yadron@wsj.com

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