It’s become a familiar sight: An agitated Sen. John McCain railing against Obama administration policies and touting his own conservative credentials. On April 15, for example, the Arizona Republican, who in a past political life opposed the 2001 and 2003 Bush tax cuts, lambasted the tax policy of his 2008 opponent in a passionate speech on the Senate floor.

“Today, all over America, there will be people demonstrating at tea parties, at gatherings, at organizations, at coffee shops, at restaurants, at places of business, at the water cooler,” McCain said, adding that voter backlash over Obama administration tax policy “will fuel the fire that is spreading across America and will culminate this coming November.”

Such sharply partisan rhetoric has become a much more familiar part of McCain’s lexicon in recent months as the once self-professed “maverick” — who recently eschewed that title — works to stave off the first formidable primary challenge of his Senate career. McCain has built upon a rightward tack he began during his failed 2008 presidential campaign, stressing his fiscal bona fides, including his long-held opposition to earmarks, while appearing to embrace more conservative stances on issues ranging from immigration to guns to gays in the military. McCain’s GOP primary opponent, former Rep. J.D. Hayworth, has dubbed McCain’s election-year posturing the “Johnny Mac shuffle” even as he bills himself as the race’s “consistent conservative.”

In a recent interview, McCain dismissed claims that he’s repositioned himself, calling them “a very convenient line” that is without merit.

“I have been accused of changing in almost every political contest that I have been in,” he said. “I understand it. But it’s not true. It’s not justified by the facts. … When I went against the spending practices of the Bush administration, I’m a maverick. When I go against the spending practices of the Obama administration, I’m a partisan. OK? I’ve always done what I think is right for the state of Arizona and the country.”

Sticking to His Guns

One realm in which the Arizonan has stuck to his guns — and earned respect from both sides of the aisle — is the Armed Services Committee, where he has served as the ranking member since 2007. From that perch, McCain, who pressed President George W. Bush to send more troops into Iraq before the 2007 surge, has not been slow to speak out when he has disagreed with Obama administration policies, as he did late last year when he criticized Obama’s plan to begin withdrawing troops from Afghanistan by July 2011.

“I still have to have my honest opinion,” McCain said recently when asked whether it was awkward for him to go against the man he fought for the presidency.

McCain noted that prior to the surge he had “strongly disagreed with President Bush on troop levels in Iraq.”

“I have to do what I think is right,” he said. “There’s no equivocation on a national security issue.”

But sometimes lately, McCain’s moral compass has seemed to lead him in a somewhat different direction than it has in the past. In February, he appeared to back away from his earlier support for repealing the “don’t ask, don’t tell” policy for gays serving in the military. McCain told Defense Secretary Robert Gates at a Feb. 2 hearing that he was “disappointed” in Gates’ testimony supporting repeal of the policy.

“At this moment of immense hardship for our armed services, we should not be seeking to overturn the ‘don’t ask, don’t tell’ policy,” McCain said.

McCain’s position on the issue could be in the spotlight in the coming weeks as the Senate turns to the fiscal 2011 Defense authorization bill, which the Armed Services panel spearheads.

The Arizonan also has raised concerns about the Strategic Arms Reduction Treaty that the U.S. signed with Russia in April. McCain and other Republicans are wary of Russian assertions that they could pull out of the treaty if the U.S. moves forward with anti-missile systems, fearing that Russia could hamstring plans to bolster U.S. missile defenses. McCain also has repeatedly accused the administration of shirking its responsibility to secure the border with Mexico, which McCain — who was the chief GOP architect of a failed 2007 effort to pass a comprehensive immigration bill that included a path to citizenship — has emphasized since his presidential run as the most important first step in dealing with the problem of illegal immigration.

“This is a national security issue where the United States has an unsecured border between Arizona and Mexico, which has led to violence, the worst I have ever seen, and numbers that stagger those who are unfamiliar with the issue — such as 241,000 illegal immigrants were apprehended on the Tucson sector border of Arizona in the last year,” McCain said in an April 26 floor speech.

A Sometime Obama Ally

McCain also has shown that he is willing to go to bat for an Obama cause when it’s one with which he agrees. He helped deliver Obama a major victory last year when he rallied support for an amendment to the fiscal 2010 Defense authorization bill that terminated production of the F-22 fighter jet in the face of a White House veto threat.

“I don’t think the F-22 vote would have gone the way it did if John hadn’t gotten involved,” said Sen. Lindsey Graham (R-S.C.), an Armed Services member and former military prosecutor who is McCain’s closest Senate ally. “On the defense side, it’s the same old John McCain when it comes to special interests dictating defense policy.”

And earlier this year it was McCain, not Armed Services Chairman Carl Levin (D-Mich.), who applauded Gates when Gates said he would recommend that Obama veto legislation that funds additional C-17 transport planes or an alternative engine for the F-35 fighter plane.

Indeed McCain’s willingness to side with Democrats, coupled with his deep knowledge of the Pentagon and national security policy — not to mention his personal experience as a Navy veteran and prisoner of war in Vietnam — have earned him unequivocal respect from Democrats on the Armed Services panel. Sen. Claire McCaskill said she had found common ground with McCain in the committee on issues related to government transparency and containing Congressionally directed spending, noting that she and McCain have the “same view on earmarks.”

“That makes it easy for us to conspire together about trying to get rid of the earmarks,” the Missouri Democrat said.

More Collegial Than Most

Nebraska Sen. Ben Nelson, another Democrat on the panel, said his dealings with McCain had been “fairly collegial,” in part because of the nature of the committee itself.

“Generally, the Senate Armed Services Committee doesn’t engage in a lot of partisan politics,” said Nelson, who, like McCain, was a member of the bipartisan, moderate “Gang of 14” that crafted a compromise on judicial nominations in 2005.

“That doesn’t mean that there’s not partisanship there from time to time, but it’s not the main driver. … The individual policy issues are more important than oozing partisanship. … So it makes it easier to work with people on both sides of the aisle.”

The panel’s newest Republican, Massachusetts Sen. Scott Brown, said he interacts regularly with McCain, who was an early supporter of Brown’s upstart, unlikely bid to win the seat of the late Sen. Edward Kennedy (D).

“He’s a war hero, a national treasure, and he has expertise unlike anyone else on that committee,” Brown said.

Another Republican member of the committee, Sen. Jeff Sessions, said he’s been “very impressed with John’s leadership on Armed Services and a lot of issues since he’s come back” from the presidential campaign.

“He would not have surprised me at all if he would have slowed down a bit for a while,” the Alabama Republican said. “But I haven’t seen that at all.”