Washington (CNN) -- A senior Republican senator pressed Pentagon leadership Thursday as to why nobody -- other than a very junior soldier -- has been held responsible for the leak of thousands of secret national security documents to WikiLeaks.
Sen. John McCain, R-Arizona, called the WikiLeaks episode "an incredible breach of national security."
In a tense exchange, McCain asked Defense Secretary Robert Gates whether the Pentagon has identified or punished anyone else.
"Have you held anyone responsible?" McCain asked.
"Not yet," replied Gates, who earlier said the criminal investigation limits the Defense Department's ability to conduct an independent investigation.
So far a single low-ranking U.S. soldier, Pfc. Bradley Manning, is the only person charged and held in custody in connection with the leaks.
Later McCain grilled other Pentagon officials, who were testifying with Gates before the Senate Armed Services Committee hearing on the ban on gays and lesbians serving opening in the military.
McCain appeared obviously frustrated.
"It's been since July," McCain said with a dismissive wave of his hand, referring to the first WikiLeaks release of Defense Department documents.
"Can't you carry out an investigation at the same time that the criminal investigation is going on?" McCain asked Joint Chiefs Chairman, Adm. Mike Mullen.
"Yes, sir, in certain kinds of incidents that's certainly possible," Mullen answered.
"At least, maybe, to hold someone responsible for this besides a private first class," McCain said.
Mullen said everything necessary must be done to prevent another breach of secure documents, stopping short of directly endorsing McCain's call for punitive action against WikiLeaks organizers such as travel bans, asset freezes and other sanctions.
"In my world, when I've got men and women in harm's way and they are now exposed because of this, I think we as a country should do all we can to make sure it can't happen again," Mullen said.
The political frustration was bipartisan. Following a closed-door hearing of the Senate's intelligence committee on WikiLeaks' latest release, the group's outgoing chairwoman, Sen. Dianne Feinstein, said that not enough is being done to protect critical government information.
"This qualifies as espionage," the California Democrat said as she left the hearing. "[The release] incapacitates this nation to carry out business... This is far beyond free speech."
On Thursday, Sens. John Ensign (R-Nevada), Scott Brown (R-Massachusetts) and Joe Lieberman (I-Connecticut) proposed legislation to make it easier for federal authorities to go after WikiLeaks' founder, Julian Assange, and others behind leaks of confidential U.S. documents.
"What Wikileaks has done amounts to espionage in a most serious form," said Lieberman. "It's probably the most terrible act and greatest act of espionage against the United States in our history."
Meanwhile, the U.S. government also continued its verbal assault on Assange.
"He could be considered a political actor. I think he's an anarchist, but he's not a journalist," State Department spokesman P.J. Crowley said at his daily briefing.
"Mr. Assange obviously has a particular political objective behind his activities and I think that, among other things, disqualifies him from the possibility of being considered a journalist."
Wikileaks often is referred to as a "whistle-blower" organization but the State Department spokesman shot that down, too.
"He's not a journalist, he's not a whistle-blower," Crowley said. "He is a political actor; he has a political agenda."
"He's not an objective observer of anything. He's an active player. He has an agenda, he's trying to pursue that agenda and I don't think he can qualify either as a journalist on the one hand or a whistle-blower on the other."
Assange's actions, Crowley said, affect more than just the United States.
Assange, he said, "is trying to undermine the international system that enables us to cooperate and collaborate with other governments and to work in multi-lateral settings and on a bi-lateral basis to help solve regional and international issues. What he's doing is damaging to our efforts and the efforts of other governments. They are putting at risk our national interests and the interests of other governments around the world."
The Pentagon's top lawyer, Jeh Johnson, said WikiLeaks has openly solicited people on its web page to break the law and provide classified information.
"I don't view WikiLeaks as journalism," said Johnson. Johnson said he was briefed regularly on the open criminal investigation by the Department of Justice.
"I worry [WikiLeaks] is out trying to solicit others right now for additional information," Johnson said.
But legal experts say whether the government considers it a journalistic organization or not, WikiLeaks will benefit from the same legal protections as mainstream media.
Baruch Weiss, a former federal prosecutor and now a partner with the Washington-based law firm of Arnold & Porter, told CNN that there has never been a successful U.S. prosecution of a media outlet for espionage, including in situations such as the then-controversial publication of the Pentagon Papers in the early 1970s.
"Nobody brought any charges against the New York Times when it disclosed the Pentagon Papers. They tried to prosecute Daniel Ellsburg, who was the individual who disclosed it -- the prosecution fell apart, Weiss said. "These prosecutions don't work."
Weiss in 2009 successfully defended two former pro-Israel lobbyists who had been charged with espionage. Charges were dropped by prosecutors in that case after a court ruling that would have allowed the defense to use more classified information at trial than the government had wanted.
"WikiLeaks may not sound like the media, but it is," said Weiss. "For legal purposes, for First Amendment purposes, it's publicizing information. It's putting it out there for the public so that people can decide whether the government's doing a good job or a bad job as it conducts our foreign policy.
As for portraying WikiLeaks as a spy organization, Weiss said that would be "tough."
"A juror sitting in the box, when he hears spy, or espionage ... is going to be thinking about a hand-off in a cemetery in the middle of the night, a hollow tree stump, people tip-toeing around, and that's not what we have here. Julian Assange got this information, WikiLeaks got this information and said, 'We got this information. We think it's important for the world to know,' and they posted it."
CNN's Jill Dougherty and Mike Ahlers contributed to this report.