WASHINGTON – The political dust-up over the FBI handing documents about the Hillary Clinton email investigation to Congress is intensifying, with Republicans complaining the materials were turned over in such a way that assessing them is difficult and Democrats contendingthey should not have been given to legislators.

On Tuesday, the FBI delivered to Congress an overview of the investigation along withsummaries of more than a dozen interviews with senior Clinton staffers, other State Department officials, former secretary of state Colin Powell and at least one other person, according to an email from a senior aide to Sen. Charles Grassley (R-Iowa) that was sent to congressional offices.

The tussle centers over whether the FBI has the authority to impose sharp restrictions on the material, which co-mingled classified and nonclassified documents. The FBI required Congress to maintain the materials in a secure area accessible only by those who have clearances. Also at issue is the aim of Grassley and other Republicans to publicly release the summaries, which include new, unclassified details about the FBI's server investigation.

In announcing the agency's findings last month, FBI Director James Comey said the investigation was untainted by political influence. Comey has said he wants to release more details than normal about the agents' work to underscore the nonpartisan nature of the probe. But the unusual delivery of the records, and the restriction imposed by the FBI, have fueled the partisansquabble.

"I certainly don't think it was done to feed the political fire; I think it was done, as the director said, in the interest of transparency," said Rep. Adam Schiff (California), the ranking Democrat on the House Intelligence Committee. "But while that might be a good thing in the short term for the bureau, I think it's very problematic in the longer term for the entire Department of Justice."

The FBI declined to comment for this article. Ron Hosko, a former assistant director at the FBI, said Comey has "spoken repeatedly on his respect and understanding" of congressional oversight, and that is probably why the director was so responsive to legislators' inquiries.

"There is an oversight responsibility. There is an undeniable political piece of this thing," Hosko said. "I don't see Comey or the FBI trying to push back and say, 'You're not entitled to X' if the law says they are."

Comey announced last month that he was recommending that Clinton not be charged in connection with her use of a private email server while she was secretary of state, offering an unusual level of candor at a news conference in which he opined that she was "extremely careless" in her handling of classified information. He later promised to release some materials to Congress.

Matthew Miller, a former Justice Department spokesman who has worked for several Democratic campaigns, said that although Comey might have been seeking to burnish his reputation for honesty, he ultimately treated Clinton unfairly and set a potentially dangerous precedent for future high-profile cases. Witnesses, Miller said, might be less likely to come forward – and agents and prosecutors tempted to work differently – knowing Congress would one day have access to what they said and did.

"That's obviously not how the FBI is supposed to work," Miller said.

And Comey's release has not mollified Republicans who want more information. Rep. Jason Chaffetz, R-Utah, the House Oversight Committee chairman, said he was concerned about what was not included in the binders full of documents, and he continued to question Comey's conclusion that Clinton should not be charged.

"This whole case is upside down and backwards," Chaffetz said. "There's nothing normal about it."

Grassley and his staffers have complained to the FBI that the unclassified material released to Congress was mixed with classified material, making its review and possible release burdensome.

The staffers and officials whose interview summaries are unclassified include longtime aide Huma Abedin; former chief of staff Cheryl Mills; former campaign staffer Heather Samuelson, who helped sort Clinton's emails so they could be produced publicly; and former IT staffer Bryan Pagliano, who set up a server in Clinton's home, according to the email from the Grassley staffer.

Summaries also include Powell, Under Secretary of State for Management Patrick Kennedy; former assistant secretary for diplomatic security Eric Boswell; and former executive secretary Stephen Mull, according to the email. Powell, who also used a private email account while secretary of state but not a private server in his home, wrote in an email that he had "a pleasant interview with two agents."

"It was less about the specifics of emails than the whole process of how they are handled and how to manage info flow in the future," Powell wrote.

Fewer than "a dozen and a half paragraphs" of the FBI's 32-page investigative summary also are marked as secret, according to the Grassley staffer's email.

It remains unclear whether that summary will be released, even if Congress is able to separate classified portions from the unclassified material.

On Wednesday, Grassley, the Judiciary Committee chairman, wrote to Michael DiSilvestro, director of the Office of Senate Security, asking him to separate the classified materials from the nonclassified ones. Grassley had earlier told a Washington Post reporter he hoped the non-classified would be made public eventually. But DiSilvestro wrote back Thursday that the FBI had provided the material with a "handling restriction" that all of it be kept in his office, and the Judiciary Committee and the FBI would have to negotiate different terms.

On Friday, Grassley wrote back that his committee had not agreed to such restrictions on nonclassified material, and it would be "inappropriate" for DiSilvestro to let the FBI dictate what could be done with it.

"Absent such prior agreement, there are serious Constitutional separation of powers issues raised by the Executive Branch purporting to instruct a Senate office how to handle unclassified, nonnational security information," Grassley wrote. "It's unclear how the Executive Branch would have any authority to do so."

DiSilvestro's office referred a reporter to the Senate secretary. A representative there did not return a message seeking comment.

Brian Fallon, a spokesman for Clinton's campaign, has said the handing over of documents was "an extraordinarily rare step that was sought solely by Republicans for the purposes of further second-guessing the career professionals at the FBI." But, he added that "if these materials are going to be shared outside the Justice Department, they should be released widely so that the public can see them for themselves, rather than allow Republicans to mischaracterize them through selective, partisan leaks."