In a preview of a debate McCain hopes to keep from reaching the Senate floor for a vote this month, opponents vehemently rejected a 10-month Pentagon study that found there would be minimal disruption in the ranks if Congress repealed the "don't ask, don't tell" policy.
At a hearing of the Senate Armed Services Committee, they told Pentagon leaders they did not take seriously enough resistance from Army and Marine Corps combat and special-operations units. They also questioned whether the Pentagon survey of 115,000 troops was large enough to be representative.
The often-testy exchange with Defense Secretary Robert Gates and Adm. Michael Mullen, chairman of the Joint Chiefs of Staff, both strong advocates of repeal, offered a warm-up to the fireworks expected Friday. That's when the more skeptical service chiefs, who have publicly spoken out against changing the policy, appear before the same panel.
Two days after the Pentagon released the study, Gates reiterated the need for Congress to act this month to repeal the policy before a judge does.
Noting recent court decisions to overturn the ban, he said repeal must be done over time but worried that it could be "imposed immediately by judicial fiat -- by far the most disruptive and damaging scenario I can imagine, and the one most hazardous to military morale, readiness and battlefield performance."
He warned, "Those that choose not to act legislatively are rolling the dice" and later asked, "If not now, when?"
At least one Republican, Maine Sen. Susan Collins, appeared sympathetic. She rejected the argument of colleagues who said wartime was the wrong time to make the change, noting racial integration of the military was carried out during the Korean War.
She also dismissed the idea that service members should have been asked directly what they thought. "I would point out that our troops aren't asked whether they should be deployed to Afghanistan. They're not asked if we should have a war in Iraq. They're generally not asked about policy decisions," she said.
Collins, a moderate Republican who has not said how she would vote, said the study offered ample information about attitudes. She quoted a special operations force war fighter cited in the report who said, "We have a gay guy [in the unit]. He's big, he's mean and he kills lots of bad guys. No one cared that he was gay."
Gates, Mullen and the co-authors of the study, Pentagon General Counsel Jeh Johnson and Army Gen. Carter Ham, testified they were confident that any problems could be dealt with through strong leadership and training. Gates said he would not sign on unless he was certain the military was ready.
Mullen sought to assure the lawmakers, saying the study -- which gay rights advocates had opposed as a form of foot-dragging -- had proved arguments against repeal are wrong.
"Repeal of the law will not prove an unacceptable risk to military readiness. Unit cohesion will not suffer if our units are well-led. And families will not encourage their loved ones to leave the service in droves," he testified. He added that while he did not find the concerns of combat and special forces troops "trivial or inconsequential," they would be mitigated by "effective, inspirational leadership."
Recalling he had served without incident with gay sailors aboard a destroyer off the coast of Vietnam, Mullen said, "I would not recommend repeal of this law if I did not believe in my soul that it was the right thing to do for our military, for our nation and for our collective honor."
Gates said implementation would not be problem-free. "We have to be honest and straightforward," he said, drawing on the experience of blacks and women in being integrated into the military. Just as racial problems lingered into the Vietnam era and even as sexual assault of female service members continues today, "These social changes in the military have not been easy."
But the concerns of combat troops "do not present an insurmountable barrier" to repeal, he insisted, and said there would be "an abundance of care and preparation" to train and acclimate "those serving at the tip of the spear in America's wars."
McCain parried back angrily when Gates suggested a naivete on the part of many combat troops, most of whom are in their 20s or younger and have never served with women either.
"I couldn't disagree more," McCain growled. "We send these young people into combat, we think they're mature enough to fight and die. I think they're mature enough to make a judgment on who they want to serve with and the impact on their battle effectiveness."
Gates did not back down when McCain said large numbers of combat troops would leave the military if gays were allowed to serve openly.
While Johnson said the Pentagon "should assume we will lose some of our chaplains" who view homosexuality as beyond the pale, Gates dismissed the prospect of tens of thousands of homophobic service members departing in the midst of two wars.
"It isn't like they can just say, 'I'm outta here.' They are going to have to complete their obligations" under the terms of their enlistment or contract for officers, he said.
Gates cited the experience of 35 other countries that already allow gays to serve openly. He noted that surveys of British and Canadian troops also resulted in dire predictions of mass exits and yet few troops left when the ban on gays was lifted.
Sen. Saxby Chambliss of Georgia said he was "really bothered" by Gates' response, suggesting a cavalier attitude.
"If I believed a quarter-million people would leave the military immediately I would certainly have second thoughts," Gates said, adding that he did not.
While McCain and other Republicans repeatedly cited the findings in highlighting the unease in all-male ground combat units, they also downplayed the study's reliability. They noted that of 400,000 surveys sent out, "only" 115,000, or 28 percent, were returned.
Advocates for repeal filled the hearing room. One, a member of the group Code Pink, held a sign reading, "McCain is a bigot."
The ranking Republican on the committee, whose own family has spoken in favor of repeal, has been accused by rights advocates of flip-flopping on the issue and constantly moving the goal posts for his support.
McCain appeared to address such critics in his opening remarks.
"As we move forward with our discussion on this, I hope that everyone will put aside political motives and agendas," he said to snickers in the audience. "I also hope that everyone on both sides can refrain from questioning people's integrity."