A man takes a picture from the top of a bus at a rally for the Tea Party Express national tour last year. (Photo by Spencer Platt/Getty Images) (Spencer Platt)

The tea party movement, which established its power last year by defeating Republicans who didn’t meet its idea of what a conservative should be, is shifting to focus more on policy as its leaders try to expand its growth and effectiveness.

The strategy appears to be working, both on the presidential campaign trail, where most Republican candidates are eagerly embracing tea party priorities, and in Washington, where loyalists are setting the terms of the debate over taxes and spending.

On Capitol Hill, lawmakers elected in the tea party wave of 2010 helped grind the debt-ceiling negotiations to a halt with their objections to any deal that includes more taxes. The more vocal among them question the establishment wisdom that a default on the federal debt would precipitate an economic catastrophe. And they have pushed many of the presidential contenders to adopt similar points of view.

At a campaign appearance in Iowa on Monday, former Minnesota governor Tim Pawlenty said Republicans in Congress should use the debt-limit debate to achieve deep budget cuts and long-term spending reforms. Failing that, he has said, lawmakers should allow the country to default.

Rep. Michele Bachmann (Minn.), appearing Monday in Columbia, S.C., signed her own version of Sen. Jim DeMint’s “Cut, Cap and Balance” pledge (the House passed a bill echoing the South Carolina Republican’s pledge Tuesday night). To the three-part promise to cut spending enough to reduce the deficit next year, enact enforceable spending caps and approve a constitutional amendment requiring a balanced budget, Bachmann added her own line vowing to repeal and defund President Obama’s health-care legislation.

Most of the other candidates, including former Massachusetts governor Mitt Romney, have signed DeMint’s version of the pledge.

While potentially broadening its appeal, going after policies instead of people also protects the tea party movement from picking a losing fight that could sink its popularity. And it illustrates the view that defeating Obama is more important than disqualifying a Republican candidate who might be best positioned to do it.

A year ago, for instance, Romney would have been the perfect tea party target: a Republican who has called for emissions reductions to combat global warming and who, as governor of Massachusetts, signed a health-care overhaul that was a model for the landmark federal legislation.

So far, though, most tea party leaders are not directly taking on Romney — and some are even backing him.

“I don’t agree with Mitt Romney on everything,” said Rep. Jason Chaffetz (R-Utah), a darling of the tea party movement who surprised some conservatives by endorsing Romney last month. “But I want to beat Barack Obama, and I think he’s the best person to do that.”

DeMint, who endorsed Romney in his 2008 presidential bid but has stayed neutral this year, said he is “going to talk good about all the candidates, because I don’t know who is going to wind up being the nominee. None of them are going to be perfect. We’re not going to have a perfect package. What I hope is to shape the policies.”

DeMint announced this month that he will host a policy forum in September in his home state at which he expects to influence the platform and positions of the Republican field.

Similarly, Sal Russo, the founder of Tea Party Express, a political action committee, directed millions of dollars last year to knock out such Republicans as then-Sen. Robert F. Bennett of Utah and then-Rep. Mike Castle of Delaware. But this year is different, Russo said: The goal is to wrest policy promises from candidates, not to punish them for past mistakes.

“I don’t want to play ‘gotcha,’ ” he said. “I understand that people have not fully appreciated the dire conditions our country’s finances were in. They didn’t know. They didn’t understand it. But now they do.”

The tea party is hardly a monolithic entity, and some groups are focused on disqualifying Romney. Leading that charge are FreedomWorks, a Washington-based free-market advocacy group, and talk-radio superstar Rush Limbaugh. After Romney acknowledged in a recent speech that he believes humans contribute to global warming, Limbaugh quipped: “Bye bye, nomination!”

FreedomWorks ran a table at the Republican Leadership Conference in New Orleans last month with at least one top goal, organizers said: to spread the word that Romney is an unacceptable nominee.

Romney has kept some of the pressure at bay by adopting some tea party positions. In addition to signing the “Cut, Cap and Balance” pledge, he has promised to repeal Obama’s health-care law. And Romney spokeswoman Andrea Saul said he has been reaching out to tea party leaders across the country.

Those efforts have helped him earn a plurality of support among tea-party-affiliated voters, according to a recent NBC/Wall Street Journal poll.

Some of the candidates are so eager to burnish their tea party credibility that they are trying to take a leading role in pressuring leaders in Congress not to compromise in the debt-limit negotiations.

Pawlenty not only has said in speeches that the talks represent a “line in the sand” moment for conservatives, but members of his campaign staff have reached out to Republican House leaders to urge them to stay the course.

Bachmann, who leads the House Tea Party Caucus, has said repeatedly that she will vote against increasing the debt ceiling — a potentially influential stand among other tea-party-aligned House members.

Former senator Rick Santorum (Pa.) has said he “absolutely” would let the nation default rather than raise the debt ceiling without spending concessions. Former businessman Herman Cain and Rep. Ron Paul (Tex.) have taken similar stands.

Romney has not gone so far, saying he would agree to an increase in the debt limit, but only with major reductions in the size of government.

Assiduously courting the tea party comes with a certain amount of peril. Tacking too far to the right to win the nomination risks alienating independent voters in the general election — always a challenge in tough primaries — and this seems a particular risk this year. Democrats, meanwhile, are already positioning to take advantage of it.

“Threatening to let the nation default may make for good tea party politics,” said Bill Burton, the former deputy White House press secretary who is running a pro-Obama super-PAC, Priorities USA. “But it’s not good for the nation, and it won’t be good for Republicans when they get to general elections.”

Some conservatives haven’t ruled out a more aggressive campaign to block Romney’s nomination. Brendan Steinhauser, state director for FreedomWorks, said the group would consider backing off if Romney apologized for the Massachusetts health-care bill. Otherwise, promoting someone else, say Bachmann or Pawlenty — or going after Romney in such critical early states as South Carolina, Florida and Nevada — remains an option.

“You talk to people who are smart and principled and conservative, and they all say, ‘Look, we’ve got to have the most conservative candidate who can win,’ ” Steinhauser said. “They’re looking for an alternative to Obama, but they’re also looking for an alternative to Romney. I think people will galvanize behind an alternative.”

Staff writer Philip Rucker contributed to this report.