WASHINGTON (Reuters) - Republican Representative Michael Grimm's office was filled with conservative Tea Party activists one day last month and they weren't happy.
Why, they asked, hadn't the first-term lawmaker done more to slash U.S. government spending? Why, months earlier, had Grimm broken ranks with the Tea Party by voting - with another 173 of the House's 242 Republicans - to raise the U.S. debt limit?
Grimm, 42, said he did not want to raise the debt limit beyond $15 trillion but that it was either that or shut down the government.
"When you are in the middle of a war, how do you close the government and not pay your soldiers?" the former Marine and FBI agent said. "How do you not send seniors Social Security checks?
"I'm frustrated, too," Grimm recalled telling the activists.
The scene in Grimm's office was a vivid display of the pressure facing many of the 87 House Republican freshmen - most backed by the Tea Party - as they seek re-election nearly two years after they swept into Washington and helped change the national debate on government spending.
In the November 6 elections, Democrats are targeting Grimm and more than two dozen other Republican freshmen by casting them as the compromise-resistant sources of division and dysfunction for an unpopular Congress.
But as the recent episode in Grimm's office showed, some of the most intense pressure facing Republican freshmen is coming not from Democrats but from the Tea Party activists who helped send them to Washington in the first place.
If 2010 was the year the Tea Party emerged as a political force in Washington, 2012 will be the year that determines whether the movement can live with itself on Capitol Hill.
The activists complain that Republicans have not been tough enough in resisting increased government spending and that they have become part of the Washington bureaucratic culture that the Tea Party despises.
Several House freshmen - including Ann Marie Buerkle of New York, Allen West of Florida, Robert Dold, Bobby Schilling and Joe Walsh of Illinois, Chip Cravaack of Minnesota and Dan Benishek of Michigan - represent districts that are politically divided or leaning only slightly toward the Republican Party.
For them, a lack of enthusiasm among Tea Party members who have backed them in the past could lead to defeat in November.
Still, the vast majority of Republican freshmen are expected to win re-election - and help their party keep control of the House - largely because they are from conservative districts.
The nonpartisan Cook Political Report estimates that about two dozen of the first-term Republicans face competitive races.
Grimm, who represents New York City's Staten Island, is a slight favorite to win another term over Democrat Mark Murphy, Cook projects.
Even so, Grimm is among several freshmen Republicans who are receiving a lecture from Tea Party activists that goes something like this: Remember why you're in Washington.
"We have passionate, knowledgeable and diverse members," said Frank Santarpia, an organizer of the Staten Island Tea Party, several of whose members met with Grimm in March. "Some of our members love Grimm, others are disappointed with him."
Republican Rep. Steven LaTourette, an 18-year veteran of Congress from Ohio and close friend to House Speaker John Boehner, said he respects the power of the Tea Party movement but that it has made it difficult to accomplish much in the House.
However, LaTourette said, many freshman lawmakers have "grown into the job," and have become more than simply reflections of the Tea Party's no-compromise argument.
"Two-thirds (of House Republican freshmen) now realize you have to compromise to get things done," LaTourette said. "But there are about 20 who don't have any give in them and that's why we are having problems. If it smacks of spending, they will vote against it."
Some freshmen elected with Tea Party support have not totally embraced the Tea Party label since they got to Washington.
Buerkle, who is battling former Democratic Congressman Dan Maffei in her district in western New York, remains a Tea Party favorite because, among other things, she voted to shut down the government rather than increase the U.S. debt limit.
But like most other House Republican freshmen, Buerkle has declined to join the House Tea Party Caucus.
"The Tea Party is sort of disorganized," she said. "I could tell they were effective but I saw no reason to join the caucus. I think we have been very successful - not as a freshman class but as the House Republican Conference - in changing the debate and focusing attention on the deficit and the debt."
Randy Bishop, head of a Tea Party Patriots group in Traverse City, Michigan, sees his Republican congressman, Dan Benishek, a former small-town doctor from Michigan, as a "major disappointment" since he was elected to the House in 2010.
"We feel he's been co-opted by the Republican establishment," said Bishop, upset with Benishek for voting to increase the debt limit, among other things.
"I told him to his face that he should have shut the government down like (then-Republican House Speaker) Newt Gingrich did" in late 1995 and early 1996, Bishop said.
That shutdown led to a voter backlash against Republicans in 1996. Benishek said he did not believe shutting the government was a viable option and feared it would backfire politically, just as it did with Gingrich.
Benishek is rated by Cook as a slight favorite to hold on to his seat; a Democratic foe will be picked in an August primary.
"Democrats are going to spend a ton of money to beat me," Benishek said. "I'm not all that partisan. I just try to do the right thing."
The clearest sign of the anxiety within the Tea Party has come from Benishek's neighbor state, Illinois, where because of congressional redistricting two Republican incumbents - freshman Adam Kinzinger, 34, and Dan Manzullo, 68, who has been in Congress for nearly two decades - faced each other in the recent Republican primary.
Tea Party activists who had backed Kinzinger in 2010 worked against him this time, saying he had not moved aggressively enough to cut spending.
But Kinzinger had a key advocate: House Majority Leader Eric Cantor, who directed his political action committee to spend $25,000 to back Kinzinger, who easily won the primary.
Among those Republicans on the Democrats' target list in the House is Jeff Denham, a farmer and Air Force veteran who previously served eight years in California's legislature.
Two weeks after he was elected to the House in 2010, Denham was asked by a liberal blogger whether he would vote against increasing the government's debt ceiling.
"Absolutely yes," Denham said.
Nine months later, Denham voted to increase the debt ceiling. He quickly flew back to California and held a meeting with Tea Party leaders and other constituents to explain why.
"I laid it all out for the people in my district," Denham said, adding that he reluctantly backed an increase to avoid a crippling government shutdown.
Denham said he wants to keep a good relationship with the Tea Party.
"He understands that the Tea Party is vital to the success of the freshman class," said Brian Du Bois, 38, a leader of the Modesto, California, Tea Party Patriots.
The group's passion for Denham could be crucial in what could be a close race.
Because of redistricting, his constituency is now more Democratic than it was in 2010. Denham's Democratic foe will be Jose Hernandez, a former NASA astronaut whose parents were migrant farm workers from Mexico.
Tea Party members in Denham's district said they will try to make sure that he does not get too comfortable in Washington.
"We're all worried those freshmen Tea Party folks have gone there and may be corrupted," said Jan Etheridge, 62, a retired federal worker and member of the Modesto Tea Party Patriots.
Tea Party-backed House freshmen not inclined to compromise on spending issues said they sometimes have felt let down by fellow Republicans.
"Sure, there have been plenty of disappointing moments," said Louisiana Representative Jeffrey Landry, a freshman whose conservative voting record earned him praise from the Tea Party-aligned group FreedomWorks and an easy path to re-election in his Gulf Coast district.
"If America would send all 87 of us back (to the House) next year," Landry said, "I think it would be a great investment."
(The story was corrected to remove "Tea Party" from beginning of paragraph 11 and replace with "House")
Editing by David Lindsey and Bill Trott