WASHINGTON -- Sen. John McCain's latest feud with the tea party senators he infamously branded "wacko birds" has prompted many to question why the Arizona Republican is seemingly intent on chastising members of his own party.

Some Capitol Hill observers have likened McCain's often frosty relationship with Sens. Ted Cruz (R-Texas), Rand Paul (R-Ky.), Mike Lee (R-Utah) and Marco Rubio (R-Fla.) to a grudge. McCain is trying to burnish his legacy, the analysis goes, even if it requires partnering with President Barack Obama, and the younger firebrand conservatives are getting in his way. New York Magazine's Jonathan Chait also suggested last week that the root of McCain's frustration is his "foreign policy hawkishness."

But one potential source of intra-party tension is being overlooked: McCain is trying to preserve the filibuster reform deal he helped shape -- and his vision of how the Senate should work.

The modest rule changes agreed upon by Senate Majority Leader Harry Reid (D-Nev.) and Minority Leader Mitch McConnell (R-Ky.) in January most closely resembled a bipartisan proposal co-sponsored by McCain and Sen. Carl Levin (D-Mich.). In addition to serving as a counterproposal to more progressive demands, the McCain-Levin package also sought to avoid a scenario in which Democrats utilized the so-called nuclear option -- that is, to change the rules via a simple majority of 51 votes on the first day of the congressional session.

But that bipartisan deal has done little to overcome GOP obstructionism in the Senate, leading Reid to float the possibility that he might revisit the nuclear option. Although Reid's threats have mostly pertained to repeated Republican efforts to block Obama's judicial nominees, McCain told reporters last week that his GOP colleagues' latest objection -- to appointing budget conferees without preconditions that the debt limit not be raised -- will only give more credence to supporters of the nuclear option.

"It will give more momentum to those who want to go to 51 votes, there's no doubt about that," McCain said, adding that the Senate's budget conferees could be told not to discuss the debt limit under a motion to instruct. "That's the way the regular order works around here. You just don't say, 'No, I object to going forward.'"

He also told The Huffington Post in a brief hallway interview last week that the same group of conservative senators had threatened to filibuster debate on gun control legislation. It's not just about regular order, McCain said, but also about how Americans view the Republican Party.

"They had planned, the same people, on filibustering the gun bill and not moving forward with it for debate, and finally it was enough of us that prevailed that we moved forward with debate," McCain said. "Think how the American people would have reacted if we hadn't even agreed to debate the gun bill?"

The senator sounded a similar warning in a Senate floor speech this past Thursday.

"If we continue to block things like this and block what is the regular order, then the majority will be tempted to change the rules of the Senate," McCain said. “That would be the most disastrous outcome that I could ever imagine."

"Are the American people unhappy with us?" he added. "Of course they're unhappy with us, because they don't see us accomplishing anything."

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