Republican Sen. John McCain's standoff with the White House over treatment of detainees — an issue the former POW knows intimately well — threatens to exacerbate his already contentious relationship with conservatives.

The Arizona senator has been a staunch supporter of
President Bush on the Iraq war. He has alienated conservatives, however, for opposing a constitutional amendment banning same-sex marriage and supporting federal expansion of embryonic stem-cell research.

Social conservatives also have taken issue with his effort to overhaul the immigration system, in part, by granting millions of illegal immigrants a path to eventual citizenship, and his work with a rogue group of senators to avert a Senate fight over Bush's judicial nominations.

As the clash escalated, McCain shrugged off suggestions that the dust-up could hurt him politically, telling reporters last week that his "credibility with the American people is that I do what I think is right."

Long known as a maverick, McCain's latest tussle with the White House is over the president's insistence that Congress allow the
CIA to use aggressive methods against terrorism suspects.

McCain and a growing group of Senate Republicans contend the United States must adhere strictly to the Geneva Conventions international standards.

Bush wants Congress to quickly pass his own proposed legislation authorizing military tribunals for detainees and harsh interrogations of terror suspects. Last week, he singled out McCain, a rival for the presidential nomination in 2000, making clear whom he blamed for standing in the way.

A year ago, McCain led a high-profile charge in Congress to clarify a law against torture by extending it to also ban cruel, inhuman and degrading treatment of prisoners. The White House issued a veto threat.

But McCain, a former Navy pilot tortured during nearly six years of imprisonment in Vietnam, attracted enough support in the House and Senate to override a veto. After a very public spat, the White House and McCain reached an agreement that essentially resulted in the senator getting what he wanted. Bush signed the bill in December.

Traveling in politically pivotal New Hampshire over the weekend, McCain again was the target of conservatives' ire — this time because of his interrogation position.

The editorial page of the Manchester Union-Leader accused McCain of "blocking our ability to gain from terrorist captives the vital information we need to fight a war in which the enemy strikes us here at home from multiple locations around the world."

Sixteen months from presidential primary season, some Republicans believe McCain's latest haggling with the White House won't have lasting negative implications.