A Clinton campaign spokesman alleged I. Charles McCullough III, the inspector general for intelligence agencies, was intentionally leaking seemingly damaging information in collusion with Senate Republicans.
But McCullough is hardly an obvious target for that accusation. An Obama appointee, he was approved in the position back in 2011 with unanimous consent by a majority-Democratic Senate.
The episode is significant given it has sidetracked her presidential campaign, where Clinton is locked in a close Democratic primary race just days before the first caucusgoers go to the polls.
The spat started Tuesday, when a letter from McCullough III to members of the Senate was leaked to the media, revealing the existence of "several dozen" cases of classified information.
That led Clinton and her campaign team to suggest the leak was an act of political sabotage, and to insist she never violated rules regarding preservation of information.
"It doesn't change the fact that I never sent or received any material marked classified," Clinton told CNN's Wolf Blitzer on "The Situation Room" on Thursday.
On Wednesday, a spokesman for Clinton's presidential campaign went so far as to claim McCullough was working with Senate Republicans to leak misleading information in an attempt to discredit the candidate.
"Two months ago, there was a political report that directly challenged the finding of this inspector general," Brian Fallon told CNN's Alisyn Camerota. "And I don't think he liked that very much. So I think he put two Republican senators up to sending him a letter so he would have an excuse to resurface the same allegations he made back in the summer that had been discredited."
Then on Thursday, Fallon seemed to backtrack a bit, admitting he didn't know whether McCullough leaked the letter, but suggesting he still bore responsibility for the fact it was leaked.
"It's quite inappropriate that he even sent the letter to Congress while this Justice Department review is going on," Fallon told CNN's Jake Tapper on "The Lead." "Did he leak the letter directly? Probably not. Did he have every expectation that was going to be leaked to whom he sent it? Probably."
McCullough's office would not comment on the allegations, but said it mischaracterized the role the inspector general's office is playing in reviewing the emails.
A spokesperson for McCullough's office told CNN, "We're not the ones making the determinations" about what's classified.
That job falls to intelligence professionals who are vetting the emails as part of an inter-agency review process, the spokesperson said, asking not to be named, adding that these individuals flagged the information as having originated in classified intelligence documents.
Furthermore, the inspector general's office has "made no classification determinations on the content or the emails in question," the spokesperson said.
The spokesperson wouldn't comment on Fallon's accusations, except to dismiss their importance.
"Obviously, we're aware that they've been saying that for a couple of days now, but we're very focused on the serious work that we have to do," the spokesperson said. "We don't even really have time to entertain that type of stuff."
The spokesperson added that the inspector general's office undertook the review with "no expectation" that classified material would be found, and sent the letter in response to a request from the senators.
"The reason we're involved at all is because there is classified information," the spokesperson added, "because wherever there are intelligence community equities, and there is an oversight role to be played, that is our jurisdiction."
An ongoing debate
For her part, Clinton is once again dismissing the notion her emails contained classified information, saying the letter is a "continuation of an inter-agency dispute that has been going on now for some months."
That dispute first emerged in July, when McCullough reported a smaller number of the emails contained classified information, prompting the State Department to involve intelligence community officials into their review of the emails as they prepare to release them under the Freedom of Information Act.
The State Department disputed the claim at the time, suggesting there was a misunderstanding about the information in the emails, which was never considered classified at the State Department.
Deputy State Department Spokesman Mark Toner repeated that conclusion Thursday in response to the latest reports, noting, "Classification is not an exact science."
"It's not a black-and-white kind of thing," he added. "There are differing viewpoints over what should be classified and how the same information can be obtained in different ways and through different modes, and that's always, again, a discussion we welcome."
But the spokesperson for McCullough said disagreements over something as basic as whether information is classified are uncommon, and that the rules on classification are clear enough that they shouldn't be in dispute.
Generally speaking, based on the type of intelligence that produced the information, it is clear which agency owns it, the spokesperson said, and it's up to that agency to decide whether it's classified.
The discrepancies in question in Clinton's case involve information intelligence agencies claim were produced by them and should therefore have been considered classified at the outset.
More classified information could emerge
Officials at the inspector general's office and at the State Department note that the inter-agency review of Clinton's emails, which are being released to the public in monthly installments, is ongoing, and that more instances of classified information could emerge.
So far, State Department officials insist, none of the emails that have been released were marked as classified at the time they were sent, but some 1,340 have been upgraded to classified retroactively ahead of their public release and redacted accordingly.
Another 18% of Clinton's emails -- representing the final and largest batch -- are scheduled to be released next week and are still under review. The State Department says it will not speak to what's in those emails until they are released, and can't definitively say whether they'll be released in time to comply with a federal judge's January 29 deadline.
"We've acknowledged that there are other reviews and investigations into some of these broader questions," Toner told reporters Thursday, also acknowledging that the department couldn't definitively determine whether they contained information that was classified at the time, only that they weren't marked as such.
Who is I. Charles McCullough III?
The Clinton camp's allegations about McCullough's political motivations have raised some eyebrows.
McCullough, who has held the position of inspector general of the intelligence community since that position was first introduced in 2011, was nominated to the job by President Barack Obama.
His nomination hearing lasted less than an hour, and he was confirmed with unanimous consent by a majority-Democratic Senate.
Prior to taking the job, McCullough held positions under both Democratic and Republican administrations in the intelligence community, law enforcement and the Treasury Department. He was, at one point, involved in crafting parts of the Patriot Act during former President George W. Bush's administration.
At his confirmation hearing, McCullough spoke about his position on issues of classification -- the oversight of which is a critical component of his position.
Answering a question about WikiLeaks, McCullough said, "I think from an (inspector general) perspective, the greatest efficacy that we could offer would be focusing on access controls, focusing on what controls are in place to allow people to get to information, and again doing that on an (intelligence community)-wide basis to determine whether or not there were systemic vulnerabilities and risks out there that we could devise recommendations to apply across the (Intelligence Community)."
Is publicly available information classified?
A Politico report
Wednesday suggested the dispute over information in Clinton's email account stems from the forwarding of a New York Times article on use of drones.
The article, which was already in the public sphere, contained information the government considered classified, but which was widely known.
Intelligence officials tell CNN such information is supposed to be treated as classified even when it's in the context of an article.
This policy was on display in the aftermath of the WikiLeaks scandal, when troves of classified documents were published online for all to see. At that time, government personnel were advised not to open the documents, even from their home computers.
"The existence of classified information in the public domain does not relieve cleared personnel of the responsibility to protect the information entrusted to them under" Executive Order 13526, which sets the rules on such information, the ICIG spokesperson said Thursday. Under that order, "cleared personnel are not permitted to deny or confirm the accuracy or existence of classified information in the public domain."
"Above Top Secret" information at risk
Of the emails that have been released by the State Department so far, all classification upgrades have been at the lowest "confidential" or secondary "secret" level, but McCullough's letter determines Clinton also sent or received information on "Special Access Programs" or SAPs -- considered so sensitive that even security clearance holders need special permission to read about them.
This information is distinguished by the level of protections it is subjected to even for people who have the highest level of Top Secret security clearance.
A limited number of people are allowed to access information on any given SAP, so those individuals must be "read in" on the program, and sign an additional non-disclosure agreement that bars them from discussing the case with anyone.
A spokesperson for the intelligence community inspector general tells CNN that McCullough and three of his staffers -- all of whom held Top Secret security clearances -- had to be "read in" on SAPs in order to review the emails in question, and that they will be "read out" when the review is completed.