Attorney General Eric Holder’s decision to appoint two U.S. attorneys to investigate recent national security leaks came under renewed fire from Republicans today, with most saying a special prosecutor is needed to ensure the investigation is independent.

Even as Holder was rebuffing calls for him to resign from Senate Judiciary Republicans today, Sen. John McCain (R-Ariz.) took to the Senate floor to push a resolution urging Holder to create a more independent probe into the leaks of classified information. The resolution also urges the president to review the results of that effort to determine if national security was breached and how “damage can be mitigated.”

And in the Judiciary Committee, Republicans took the opportunity to ask Holder difficult questions about the leaks probe.

“Given the potential conflicts of interest with the department investigating itself, the past failures of the Justice Department to prosecute their own who admitted to classified leaks, and the attorney general’s own tepid responses to my past questions about leak prosecutions, I believe the only way to truly get to the bottom of these dangerous leaks is to appoint an independent special prosecutor,” Judiciary ranking member Chuck Grassley (R-Iowa) said.

Holder strongly defended Ronald Machen and Rod Rosenstein, the two U.S. attorneys he selected, who he said had the independence and “moxie” to follow the leads wherever the investigation goes.

Holder argued he decided against a special prosecutor because it would take too long and there is an urgent need to find who leaked classified information.

Democrats, including Sens. Dianne Feinstein (D-Calif.) and Sheldon Whitehouse (D-R.I.), backed Holder’s decision. Feinstein said a fight over how to investigate the leaks would set back the investigation, while Whitehouse defended the ability of career prosecutors to conduct an independent probe free of influence from the White House or other executive branch officials.

Under questioning from Sen. Jon Kyl (R-Ariz.), Holder said he had established a process for broaching conflicts of interest that could arise during the course of the investigation.

Holder also said that he and FBI Director Robert Mueller had already been interviewed by the investigation about whether they had any role in the leaks.

Sen. John Cornyn (R-Texas) called on Holder to resign because he believes Holder has mishandled not only the leak investigation but also a Congressional investigation into the gun-smuggling operation known as “Fast and Furious.”

McCain, who gave a dramatic floor speech a week ago that seemed to open the floodgates on the leaks issue, again railed on the administration for politicizing national security to bolster the president’s credentials in an election year.

In his floor speech today, McCain yet again did not mince words in attacking the Obama administration’s approach to discussing national security issues. McCain told an anecdote of former Defense Secretary Robert Gates, who apparently told a national security advisor to “shut the ‘f’ up” about the raid that killed Osama bin Laden.

“He responded by saying to the national security adviser ‘shut the “f” up,’” McCain said of Gates, about the White House’s “communication strategy” following the mission. “That is a devastating comment and leads one to the suspicion that things were done improperly in the revelation of these most important and sensitive programs that were being carried out and are ongoing to this day.

McCain’s resolution was co-signed by 18 Republican Senators: James Inhofe (Okla.), Roger Wicker (Miss.), Scott Brown (Mass.), Kelly Ayotte (N.H.), Rob Portman (Ohio), Susan Collins (Maine), Lindsey Graham (S.C.), John Cornyn (Texas), Richard Burr (N.C.), Pat Roberts (Kan.), Rand Paul (Ky.), John Boozman (Ark.), Johnny Isakson (Ga.), Roy Blunt (Mo.), Tom Coburn (Okla.), Chuck Grassley (Iowa), Mark Kirk (Ill.) and Saxby Chambliss (Ga.).