An FBI investigation of Hillary Clinton's conduct could extend well past the election, a former chairman of the House Oversight Committee said Sunday.

Rep. Darrell Issa, R-Calif., argued the scale of potentially wrongful activity Clinton engaged in while leading the State Department is slowing down investigators.

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"What's happening in the investigation is, I think, the FBI is running into a problem that is too much to investigate," Rep. Darrell Issa, R-Calif., told Fox News host Maria Bartiromo.

"I believe they are going to have to make a summary finding as to her violation of the national records act, her taking of the documents, and of course a classified portion," said Issa who wielded subpoena power and oversaw an investigative staff while he chaired the Oversight Committee.

"They're going to have to leave the ... coordinating her activities and President Clinton's activities and Chelsea's activities in the Clinton Foundation, they're probably going to have to leave that until after the election," Issa said.

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The FBI has been investigating the charge that Clinton mishandled classified information for nearly a year. In January, that probe reportedly expanded to look at how operations at State may have been improperly coordinated with activity at the nonprofit Clinton Foundation, and at whether the foundation benefited from the arrangement.

The prospect that Clinton or her associates could face public corruption charges related to the foundation has been largely overshadowed by the issue of whether Clinton mishandled classified information. But Issa said the focus could shift once the FBI finishes the first part of its investigation.

"The foundation business is [a] complex … series of events in which foreign governments have given large amounts of money simultaneously or nearly simultaneously," Issa said. "It's complex, it's the kind of thing that can take the FBI a long time."

Issa argued that it was going to be a hurdle for Clinton to get beyond the server issue, even if the FBI does not recommend an indictment. Clinton says nothing she emailed was classified at the time. Federal officials later designated some of the material classified or secret.

But Issa said the former secretary and the former president were familiar enough with the classification process to know better.

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"President Clinton … understands that when you and your staff are communicating things, you are creating secret documents," Issa said. "When they spoke essentially in classified terms in writing, they were creating unlawful activity.

"She's going to have answer at least for, the question not of if she's indicted or not, but has she disqualified herself from this high office where you must play by the rules or people die," Issa added.

Earlier Sunday, former Secretary of Defense Bill Gates, who served under Republican presidents and President Obama defended Clinton's handling of her email.

"If you don't have any markings on a piece of paper, it is tough sometimes to tell whether it's classified or not," Gates said.