Sen. Tom Coburn (R-Okla.), shown in 2011. (Sue Ogrocki/AP)

Congressional Republicans have splintered into generational factions over how to approach the implementation of President Obama’s landmark health-care law.

Younger GOP lawmakers are urging a shutdown of the federal government in the fall to demonstrate opposition to the law.

Some more longtime lawmakers are trying the ease the tensions.

The junior crop, composed largely of those first elected in 2010 and 2012, have circulated petitions in the House and the Senate demanding that the annual funding bills for federal agencies be allowed to lapse unless Democrats agree to withdraw money to implement the health-care law. Senior Republicans have criticized this approach, telling their younger counterparts that the shutdown strategy is misguided, and blind to the policy and political ramifications of such a showdown with Obama.

It’s the latest skirmish in a battle among Republicans that has been raging for almost three years and has grown more pronounced in recent months along generational fault lines. On Capitol Hill, the younger GOP crowd has been clashing with veterans such as Sen. John McCain (Ariz.) over its more libertarian foreign policy, and now that group is challenging more seasoned Republicans on the tactics used to fight so-called Obamacare.

Sen. Ted Cruz ( R-Texas), center, and Sen. Mike Lee (R-Utah), walk to a closed-door meeting in the Old Senate Chamber on July 15. (J. Scott Applewhite/AP)

Nowhere is the battle more pitched than on the right flank of the Senate Republican Conference, where the chamber’s longtime conservative icon, Sen. Tom Coburn (Okla.), is under fire from new GOP senators and outside groups led by the Heritage Foundation’s political arm.

“Their tactics are [a] failure. It’s a good way for them to raise money,” Coburn said in an interview Wednesday, suggesting that the outside groups are only looking for attention. “It’s a good way for Heritage to raise money; it’s a good way for others” to raise funding from activists.

Congress will adjourn Friday for a five-week summer recess and return just a couple of weeks before the Sept. 30 deadline for keeping federal agencies open. Senior Republicans have privately signaled that they want to avoid a clash over the federal budget, preferring to approve a short-term resolution that would fund the government at this year’s levels deep into fall.

GOP leaders have tried to avoid an open fight with junior lawmakers by not taking public positions on what they will advance in September. “No decisions have been made,” House Speaker John A. Boehner (Ohio) told reporters Thursday.

But the clash was on full display in the Senate, where Coburn jousted with several Republicans who have led the push for holding the line and blocking federal funding for almost every agency. They are trying to rally conservative activists to pressure the party’s elder statesmen to join the fight before Sept. 30.

“We don’t have the votes, and we are unlikely to get the votes in closed-door meetings in Washington. The only way that we win this fight is if the American people rise up,” freshman Sen. Ted Cruz (Tex.) said Wednesday in a conference call with Texas reporters.

On Thursday, Cruz — along with his other lead protagonists, Sens. Mike Lee (Utah) and Marco Rubio (Fla.) — attended a rally with tea party activists outside the Capitol urging GOP leaders to fight. Cruz will head out later this month on a 10-day trip, billed as the “Defund Obamacare Tour,” with former senator Jim DeMint (R-S.C.), who runs Heritage and is leading the campaign for a showdown over funding the new health-care law.

At issue is not opposition to the legislation, which was opposed by every Republican in the House and the Senate when it passed in 2010. If anything, GOP opposition has only grown more heated in the past three years, particularly as the most critical parts of it are set to take affect in the coming months. Party strategists have placed a bet that the 2014 midterm elections can be built around health care as a central issue, believing that its implementation will be rocky and drive voters away from Democrats.

Instead, Cruz, Lee and Rubio, along with several dozen allies in the House, believe that the best way to break Democrats is to use their House majority and filibuster powers in the Senate to simply refuse funding for federal agencies and allow them to shut down in October until Obama gives in on the health-care law.

“We must do everything we can to stop Obamacare,” Rubio said Thursday.

Senior Republicans have largely rejected such an approach, particularly those, like Coburn, who were in Washington during the shutdowns of 1995 and 1996. After the GOP trio advanced its strategy in floor speeches Tuesday, Coburn took to the floor to remind his junior colleagues that those showdowns with the Clinton White House were disastrous for Republicans and that a similar showdown was likely to lead to the same result.

Moreover, the end goal of defunding Obamacare would largely not be accomplished by shutting down federal agencies, which are funded through the annual appropriations bills, because the vast majority of that law comes through the mandatory-spending side of the federal ledger and would continue even in a shutdown scenario.

In the interview, Coburn accused the outside groups, and their congressional allies, of conceiving a plan that would “set up your base” voters for failure. He said conservative activists would have expectations raised high, donate checks to the groups, then inevitably be further angered when Republicans eventually cave and reopen the government without defunding the health-care law.

“They haven’t thought this through,” Coburn added.“I think he’s just interested in a strategic approach that he thinks works,” Rubio said

The second-term Oklahoman, first elected to the House in 1994 and the Senate in 2004, is no moderate. Five years ago this week, he landed on the front page of The Washington Post and the New York Times because Majority Leader Harry M. Reid (D-Nev.) had grown so tired of his delaying tactics on relatively popular legislation that he devoted an entire week to trying to pull an end run around the Coburn blockade.

Through his use of parliamentary tactics, the senator estimated that he has saved the government tens of billions of dollars by blocking the creation of duplicative federal offices.

“You do the hardball stuff after you’ve tried the softball stuff,” Coburn said of his tactics.

No GOP senator fought the health-care measure more strenuously. At one point, just before the Christmas 2009 holiday, he used the in­cred­ibly rare procedural move of forcing the clerks to read almost the entire legislative text of the law, gumming up the floor for several days.

He’s not alone in his belief that a shutdown showdown in September is the wrong plan. Sen. Richard Burr (N.C.), who served in the House during the 1990s, called it the “dumbest idea” he had heard. Rep. Tom Cole (Okla.), a senior member of the Appropriations Committee, said shutting down the government is one of the only ways Republicans could put their House majority on the line.

After their floor debate Tuesday, Coburn huddled with Cruz and Rubio to discuss the differing strategies. The next day, Rubio said that “of course” the tone of the talk was good and that he was happy to listen to his conservative colleague.