Arizona Sen. John McCain says the Justice Department's long-running investigation into David Petraeus could lead to his voice on national security issues being "silenced or curtailed."

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Sen. John McCain urged Attorney General Eric Holder for a "fair and timely" end to the investigation into David Petraeus

The Justice Department's two-year-old investigation followed Petraeus's resignation in 2012, citing an affair

McCain says the investigation could lead to Petraeus's voice being "silenced or curtailed"

Washington CNN  — 

Sen. John McCain is prodding the Justice Department to wrap up its two-year-old investigation into David Petraeus, the former Army general and Central Intelligence Agency director.

McCain, the Arizona Republican who will helm the Senate Armed Services Committee once new lawmakers take office in January, wrote a letter to Attorney General Eric Holder on Tuesday asking for a “fair and timely” conclusion to the case.

He questioned the pace of the investigation into whether Petraeus inappropriately shared information with Paula Broadwell, his mistress who was also writing a biography of the former leader of U.S. military efforts in Iraq and Afghanistan.

“At this critical moment in our nation’s security, Congress and the American people cannot afford to have this voice silenced or curtailed by the shadow of a long-running, unresolved investigation marked by leaks from anonymous sources,” McCain wrote.

Petraeus resigned in 2012, citing his affair. But he hasn’t faded from the public eye. He’s maintained his security clearances and backed President Barack Obama’s plan to escalate the fight against ISIS in Iraq and Syria this fall.

Timeline of the Petraeus affair

He’s also joined the investment firm KKR and has taken roles with Harvard University, the University of Southern California, the University of Exeter, Team Rubicon and the Royal United Services Institute.

McCain said he regretted wading into an ongoing investigation, and said he wouldn’t judge whether Petraeus should face charges – only that he wanted a quick conclusion.

“Without commenting on the underlying merits or anticipating the outcome of the investigation, I can conclude this is a circumstance in which the principle of ‘justice delayed is justice denied’ is certainly at play, and that this matter needs to be brought to resolution,” McCain wrote.

“Furthermore, the fact that you and others within your department have weighed-in publicly on the case raises questions about whether this investigation is being handled in a fundamentally fair and appropriate manner,” he wrote.